LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

Class 


STEAM-BOILERS 

THEIR   THEOEY  AND   DESIGN 


STEAM-BOILERS 


THEIR   THEORY  AND    DESIGN 


BY 

H.  DE  B.  PAKSONS,  B.S.,  M.E. 

CONSULTING  ENGINEER 

Member  American  Society  Mechanical   Engineers  ;   Member  American 

Society  Civil  Engineers  ;  Member  Soc.  Naval  Arch,  and  Marine 

Engineers ;  and  Professor  of  Steam  Engineering, 

Rensselaer  Polytechnic  Institute. 


THIRD  EDITION 


OF    THE 

UNIVERSITY 

OF 


LONGMANS,    GREEN,.  AND    CO 

91  AND  93  FIFTH  AVENUE,  NEW  YORK 

LONDON,  BOMBAY,  AND  CALCUTTA 
1907 


Copyright,  1903, 

BY 
LONGMANS,  GREEN  AND   CO. 

Copyright,  1905, 

BY 
LONGMANS,  GREEN  AND  CO. 

All  rights  reserved. 


First  Edition,  December,  190:>.     Second  Edition,  January,  1905. 
Third  Edition.  Revised,  October,  1907. 


ROBERT   DR^yMONO   COMPANS",    PRINTERS.    NEW   YORK. 


THIS   WORK 

IS  DEDICATED  TO 

MY   WIFE. 


196477 


PREFACE 


IN  presenting  this  book  to  the  Engineering  Profession  and  to 
fellow  students  in  practical  science,  the  Author  desires  to  state  that 
no  claim  is  made  for  originality.  In  fact  it  would  be  nearly  impos- 
sible, if  not  quite  so,  to  write  a  work  on  this  subject  which  could 
be  considered  original. 

These  pages  comprise,  in  book  form,  a  series  of  lectures  delivered 
to  the  Senior  Class  of  the  Rensselaer  Polytechnic  Institute,  Troy, 
New  York,  rewritten  and  divided  into  chapters.  The  only  original- 
ity claimed  for  the  work  is  the  effort  to  cover  such  points  as  in 
practical  office  work  may  be  found  to  be  perplexing. 

No  one  should  attempt  to  design  a  steam-boiler  until  he  has  had 
some  experience  in,  or  personal  acquaintance  with,  boiler-shop  prac- 
tice. There  are  many  things  in  the  actual  putting  together  of  the 
parts  of  a  boiler  which  cannot  be  clearly  described,  and  for  just  such 
things  even  a  short  shop  experience  would  be  most  valuable. 

The  Author  acknowledges  obligations  for  the  free  use  which  he 
has  made  of  literature  on  the  subject;  and,  while  many  references 
are  mentioned  by  name,  he  now  expresses  his  thanks  to  those  to 
whom  special  reference  has  not  been  made. 

H.  DE  B.  PARSONS. 


vn 


NOTE  ON  THE  SECOND  EDITION 


IN  preparing  this  book  for  the  second  edition,  the  Author  has 
made  some  changes  to  which  he  desires  to  call  special  attention. 

The  frontispiece  which  has  been  added  illustrates  the  dissipa- 
tion of  the  heat  produced  by  the  combustion  of  a  fuel  on  a  grate. 
The  upper  part  of  the  cut  shows  a  boiler;  engine,  condenser,  hot- 
well,  feed-pump,  and  economizer,  all  connected  by  piping.  The 
lower  part  shows  the  heat  flowing  in  streams,  drawn  to  scale, 
under  an  assumed  set  of  conditions.  Where  the  heat  is  rejected 
from  such  a  cycle,  so  as  not  to  be  recoverable,  the  streams  appear 
as  if  running  off  into  space.  In  the  cut,  the  heat  at  the  grate 
corresponds  to  the  total  heat  of  combustion  of  one  pound  of  an 
assumed  coal.  By  a  combination  of  an  engine  and  a  boiler,  it  is 
not  possible  to  transform  all  of  this  heat  into  useful  work,  as  is 
proven  by  the  study  of  thermodynamics.  From  any  boiler  or 
engine  trial,  when  sufficient  data  have  been  obtained,  a  similar 
diagram  can  be  constructed  to  illustrate  the  conditions  so  found. 

Fig.  8  illustrates  one  of  the  latest  arrangements  of  a  locomotive 
fire-box  for  burning  liquid  fuel.  The  arrangement  is  designed  to 
provide  a  thorough  mixture  of  the  oil  and  air,  and  allow  time  for 
the  combustion  to  take  place  before  the  products  are  drawn  into 
the  small  tubes  and  chilled  below  the  temperature  of  ignition. 

In  the  text,  under  Liquid  Fuels,  some  changes  have  been  made 
and  attention  called  to  the  valuable  report  of  the  Liquid  Fuel 
Board  of  the  United  States  Navy  Department,  1904. 

Fig.  20  illustrates  one  of  the  most  approved  English  methods 
for  the  brick  setting  of  a  Lancashire  boiler. 

The  general  plan  of  the  book  remains  unchanged. 

H.  DE  B.  PARSONS. 


vin 


CONTENTS 


CHAPTER  I 

PAGE 

PHYSICAL  PROPERTIES 1 

Solid  Bodies.  Fluid  Bodies.  Liquid  Bodies.  Gaseous  Bodies. 
Perfect  Gas.  Laws  of  Gases.  Heat.  Conduction.  Convection. 
Radiation.  Mechanical  Equivalent  of  Heat.  Absolute  Zero. 
Specific  Heat.  Latent  Heat.  Total  Heat  of  Evaporation.  Weight 
of  Water.  Boiling.  Relative  and  Specific  Volumes  of  Steam. 
Factor  of  Evaporation. 

CHAPTER  II 

COMBUSTION 13 

General  Conditions.  Definition.  Smoke.  Coal-gas.  Marsh 
Gas.  Olefiant  Gas.  Air.  Temperatures  of  Ignition.  Laws  of 
Avogadro.  Requirements  for  Perfect  Combustion.  Products  of 
Combustion.  Composition  of  Gases  from  Combustion.  Refuse. 
Loss  of  Unburned  Coal  in  Ash-pit.  Quantity  of  Air  Required. 
Methods  of  Firing.  Thickness  of  Fire.  Heat  of  Combustion. 
Heating  Power  of  a  Fuel. 

CHAPTER  III 

FUELS 31 

Coal.  Classification.  Anthracite.  Semi-anthracite.  Semi- 
bituminous.  Dry  Bituminous.  Bituminous  Caking.  Long-flam- 
ing Bituminous.  Lignite.  Size  of  Coal.  Culm.  Weight  of  CoaL 
Peat  or  Turf.  Wood.  Coke  and  Charcoal.  Miscellaneous  Fuels. 
Sawdust.  Straw.  Bagasse.  Protection  from  Weather.  Chem- 
ical Composition  of  Coals.  Liquid  Fuels.  Gaseous  Fuels. 

CHAPTER  IV 

FURNACE  TEMPERATURE  AND  EFFICIENCY  OF  BOILER 56 

The  Temperature.  Color  Test.  Rankine's  Method  for  Calculating. 
Dissipation  of  Heat  Generated.  Percentage  of  Heat  Utilized.  Re- 

IX 


X  CONTENTS 

PAOR 

suits.     Evaporation  per  Pound  of  Fuel  and  of  Combustible.    Practi- 
cal Efficiencies. 

CHAPTER  V 

BOILERS  AND  STEAM  GENERATORS 62 

General  Conditions.  Classification.  Horse-power.  Centennial 
Standard.  Am.  Soc.  M.  E.  Standard.  Heating  Surface.  Ratio  of 
Heating  to  Grate  Surface.  Evaportion  per  Square  Foot  of  Heating 
Surface.  Design.  Description  of  Certain  Boilers.  Water-tube 
Boilers.  Proportioning  a  Boiler  to  Perform  a  Given  Duty.  Steam 
Space.  Priming.  Water  Surface. 

CHAPTER  VI 

CHIMNEY  DRAFT 125 

Problem  of  Gravitation.  Theory  of  Peclet  as  Expressed  by 
Rankine.  Natural  Draft.  Rate  of  Combustion.  Author's  Experi- 
ence. Area  and  Height  of  Chimney. 

CHAPTER  VII 

MATERIALS 138 

Cast  Iron.  Wrought  Iron.  Rivet  Iron.  Charcoal  Iron  for 
Boiler-tubes.  Wrought  Steel.  U.  S.  Naval  Requirements  for 
Boiler  Steel.  Steel  Rivets.  Steel  for  Boiler  Braces.  Mild  Steel 
Affected  by  Temperature.  Cast  Steel.  Copper.  Brass.  Bronze. 
Muntz's  Metal. 

CHAPTER  VIII 

BOILER  DETAILS 154 

The  Shell.  Strength  of  Shell,  Longitudinally  and  Transversely. 
Factor  of  Safety.  Rules  for  Thickness  of  Shell.  Limits  of  Thick- 
ness. Arrangements  of  Plates.  The  Ends.  Rules  for  Thickness 
of  Heads.  Flat  Surfaces.  Rules  for  Flat  Surfaces.  Flues. 
Strengthening  Rings.  Corrugated  and  Ribbed  Flues.  Rules  for 
Flues  and  Liners.  Tubes.  Rules  for  Thickness.  Stays.  Rules 
for  Stays.  Girders.  Combustion-chambers.  Riveting.  Welding. 
Setting.  Bridge-wall.  Split  Bridge. 

CHAPTER  IX 
BOILER  FITTINGS 231 

Mountings  and  Gaskets.  Steam-dome.  Steam-drum.  Steam- 
superheater.  Steam-chimney.  Steam-pipe.  Stop-valve.  Dry 
Pipe.  Boiler-feed.  Injectors  and  Pumps.  Feed- water  Heaters, 
Purifiers,  and  Economizers.  Filters.  Mud-drums.  Blow-off,  Bot- 


CONTENTS  XI 

PACK 

torn  Blow  and  Surface  Blow.  Safety-valve.  Fusible  Plug.  Steam- 
gauge.  Water-gauge.  Try-cocks.  Water-alarm.  Manhole  and 
Handhole.  Grates,  Stationary  and  Shaking.  Down-draft  Grate. 
Ash-pit.  Fire-doors.  Breeching.  Uptake.  Smoke-connection. 
Draft-regulators.  Steam-traps.  Separators.  Evaporators. 

CHAPTER  X 

MECHANICAL  STOKERS 295 

Classes,  Overfeed  and  Underfeed.  Advantages.  Disadvantages. 
Results  Obtained  by  Use. 

CHAPTER  XI 

ARTIFICIAL  DRAFT 300 

Advantages.  Disadvantages.  Classification.  Selection  De- 
pends on  Local  Conditions.  Boiler  Must  be  Suited  to  Draft. 
Vacuum  and  Plenum  Systems  Compared.  Economy.  Intensity. 
Jet  in  the  Stack.  Jet  under  the  Grate.  Fans.  Power  Required. 
Closed  Ash-pit.  Closed  Fire-room.  Induced  Draft. 

CHAPTER  XII 

INCRUSTATION 310 

Scurf.  Fur.  Sludge.  Scale.  Conductivity.  Solid  Matter  in 
Water.  Analysis  of  Scales.  Behavior  of  Lime  and  Magnesium  Salts. 
Scale  Prevention.  Blowing-off.  Chemical  Agents.  Mechanical 
Agents.  Galvanic  Agents.  Surface-condensing.  Heating  and 
Filtering.  Internal  Collecting  Apparatus.  Manual  Labor. 

CHAPTER  XIII 

CORROSION.     GENERAL  WEAR  AND  TEAR.     EXPLOSIONS 319 

Corrosion.  Wasting.  Pitting  and  Honey-combing.  Grooving. 
Influence  of  Air  and  Acidity.  Galvanic  Action.  Zinc  Plates.  Ex- 
ternal Corrosion.  Dampness.  Wear  and  Tear.  Idle  Boilers.  Ex- 
plosions. Stored  Energy. 

CHAPTER  XIV 

CHIMNEY  DESIGN 327 

Object.  Selection  of  Height.  Compare  Cost  of  Stack  with  Me- 
chanical Draft.  Individual  Short  Stacks  in  Lieu  of  One  Large 
Stack.  Self-supporting  and  Non-self-supporting  Stacks.  Wind- 
pressure.  Batter.  Brick  Stacks.  Section.  Lining.  Top.  Light- 
ning. Ladder.  Leakage.  Steel  Stacks. 


Xll  CONTENTS 

CHAPTER  XV 

PAUK 

SMOKE  PREVENTION 336 

Losses  Due  to  Smoke.  Public  Nuisance.  Smoke  Ordinances. 
Requirements  to  Prevent  Smoke.  Prof.  Ringelmann's  Smoke  Scales. 
Smokeless  Fuels.  Composition  of  Smoke.  Mixing  Coals.  Air 
Admissions.  Hollow  Bridge.  Extracts  from  Report  by  Prof. 
Landreth 

CHAPTER  XVI 

TESTING.     BOILER  COVERINGS.     CARE  OF  BOILERS 345 

Object  of  Testing  New  Boilers.  Hydraulic  Pressure.  Methods 
Adopted.  Measuring  for  Changes  of  Form.  Limit  of  Test  Pressure. 
Testing  by  Steam  for  Leaks.  Boiler  Trials.  Directions  for  Calcu- 
lating some  Results.  Boiler  and  Pipe  Coverings.  Heat  Losses. 
Savings.  Care  of  Boilers. 

APPENDIX  A 
SUPERHEATED   STEAM .  361 


LIST  OP  ILLUSTRATIONS 


PAGE 

THERMAL-EFFICIENCY  DIAGRAM Frontispiece 

THE  ABSOLUTE  ZERO 5 

COMBUSTION  ON  GRATE 18 

BAGASSE  FURNACE — STILLMAN  TYPE " 38 

BAGASSE  FURNACE 39 

ROCKWELL  FUEL-OIL  BURNER,  operated  by  steam  reduced  to  between 

40  and  80  pounds 44 

LASSOE-LOVEKIN  FUEL-OIL  BURNER  (Patented),  operated  by  air  at  1^ 

pounds  pressure 44 

STEAM  SPRAY  ATOMISER  FOR  FUEL-OIL — HOLDEN  SYSTEM 46 

OIL-BURNING  LOCOMOTIVE.  Heintzelman  and  Camp  arrangement 47 

END  OF  A  PLAIN  CYLINDRICAL  BOILER 71 

HORIZONTAL  RETURN-TUBULAR  BOILER,  with  extended  or  half-arch  front  72 

HORIZONTAL  RETURN-TUBULAR  BOILER.  Front  and  section 73 

HORIZONTAL  RETURN-TUBULAR  BOILER,  with  flush  or  full  front 74 

HORIZONTAL  RETURN-TUBULAR  BOILER.  Front  and  section 75 

HORIZONTAL  RETURN-TUBULAR  BOILER,  with  a  link  suspension 76 

HORIZONTAL  RETURN-TUBULAR  BOILER.  Section 77 

UPRIGHT  OR  VERTICAL  BOILER 81 

UPRIGHT  OR  VERTICAL  BOILER,  with  submerged  tube-sheet 82 

MANNING  VERTICAL  BOILER 84 

MANNING  VERTICAL  BOILER.  Sections 85 

FLUE  AND  RETURN-TUBULAR  BOILER 86 

FLUE  AND  RETURN-TUBULAR  BOILER.  Front  view  and  section 87 

FLUE  AND  RETURN-TUBULAR  BOILER.  Back  view 88 

CORNISH  BOILER 89 

CORNISH  BOILER.  Front  view  and  section 90 

LANCASHIRE  BOILER 91 

LANCASHIRE  BOILER.  Front  view  and  section 92 

GALLOWAY  BOILER,  with  expansion  rocker  support 93 

SECTIONS  OF  GALLOWAY  BOILER 94 

LANCASHIRE  BOILER,  with  Galloway  tubes 95 

LANCASHIRE  BOILER.  Sections 96 

SCOTCH  BOILER,  single-ended,  with  common  combustion-chamber 97 

xiii 


xiv  LIST  OF  ILLUSTRATIONS 

PAGE 

SCOTCH  BOILER.     End  view  and  section 98 

SCOTCH  BOILER,  single-ended,  with  separate  combustion-chambers 99 

SCOTCH  BOILER.     End  view  and  section 100 

DOUBLE-ENDED  SCOTCH  BOILER 101 

ADMIRALTY  OR  GUNBOAT  BOILER 102 

ADMIRALTY  OR  GUNBOAT  BOILER.     Sections 103 

MARINE  BOILER.     Front  end  and  section 103 

MARINE  BOILER  WITH  STEAM-DRUM 104 

SCOTCH  BOILER  WITH  STEAM-DRUM 105 

SCOTCH  BOILER.     End  view  and  section 106 

MARINE  BOILER  WITH  STEAM-DRUM. 107 

LOCOMOTIVE  BOILER 108 

LOCOMOTIVE  BOILER.     Sections 109 

BABCOCK  AND  WILCOX  BOILER 112 

BABCOCK  and  WILCOX  BOILER.     Front  view  and  section 114 

STIRLING  BOILER 115 

ALMY  BOILER 116 

NICLAUSSE  BOILER 117 

BELLEVILLE  BOILER 118 

THORNYCROFT  BOILER 119 

THORNYCROFT  BOILER.     Front  view  and  section 120 

YARROW  BOILER 121 

CHIMNEY-DRAFT 128 

STRENGTH  OF  SHELL  TO  RESIST  BURSTING  PRESSURE 155 

FLUE  STRENGTHENING  BY  ANGLE  RING 172 

FLUE  STRENGTHENING  BY  TEE  RING 173 

FLUE  STRENGTHENING  BY  TEE  RING  JOINT 173 

FLUE  STRENGTHENING  BY  FLANGING.     (Two  styles.) 173 

FLUE  STRENGTHENING  BY  THE  BOWLING  HOOP 174 

FLUE  STRENGTHENING  BY  THE  ADAMSON  RING 174 

FLUE  STRENGTHENING  BY  GALLOWAY  TUBES.      (Two  views.) 174 

Fox's  CORRUGATED  FURNACE  FLUE 175 

MORISON'S  SUSPENSION  FURNACE  FLUE 175 

PURVES'  RIBBED  FURNACE  FLUE 176 

PROSSER'S  TUBE  EXPANDER 190 

DUDGEON'S  TUBE  EXPANDER 190 

EFFECT  OF  EXPANDING  THE  TUBE  ENDS 190 

FERRULES  FOR  TUBE  ENDS 191 

RETARDER  FOR  TUBES 192 

ACME  REFRACTORY  CLAY  RETARDER  FOR  USE  WITH  FUEL  OILS 193 

SERVE  TUBE 194 

SCREW  STAY,  ends  upset  and  riveted 195 

SCREW  STAY,  ends  upset  and  fitted  with  nuts 195 

SCREW  STAY,  ends  not  upset,  fitted  with  nuts  and  washers 195 

STAY  FITTED  WITH  FERRULE. 195 

LARGE  STAY  END  WITH  NUT  AND  WASHER 196 


LIST  OF  ILLUSTRATIONS  XV 

PAGE 

LARGE  STAY  END  WITH  DOUBLE  NUTS 196 

STAY  END  WITH  BOLT  IN  DOUBLE  SHEAR 197 

NUT  FOR  STAYS,  showing  packing  groove 197 

STAY  END  WITH  BOLT  IN  DOUBLE  SHEAR.  (Two  views.) 197,  198 

A  METHOD  OF  FAILURE 198 

GUSSET  PLATE  STAY 199 

STAY  END  FITTED  TO  STIRRUP  TO  DISTRIBUTE  THE  SUPPORT 199 

STAY  END  SPLIT  TO  FORM  STIRRUP  TO  DISTRIBUTE  THE  SUPPORT 200 

DIAGONAL  STAY,  with  rivets  through  palm  in  tandem  and  in  parallel.  .  .  .  200 

HUSTON  FORM  OF  STAY  WITHOUT  WELD 201 

GIRDER  STAY  FOR  SUPPORTING  CROWN-SHEET 201 

GIRDER  STAY  FOR  SUPPORTING  CROWN-SHEET,  showing  three  forms  of 

strengthening  stays  to  shell 202 

SINGLE  RIVETED  LAPPED  JOINT 208 

DOUBLE  RIVETED  LAPPED  JOINT 209 

SINGLE  RIVETED  LAPPED  AND  STRAPPED  JOINT 210 

SINGLE  RIVETED  BUTT  JOINT,  with  single  or  double  straps 211 

TREBLE  RIVETED  BUTT  JOINT,  with  straps  of  unequal  widths 212 

JOINT  BETWEEN  TUBE  SHEET  AND  FURNACE  FLUE,  showing  countersunk 

rivet  where  exposed  to  the  fire 213 

GOOD  AND  BAD  CALKING 215 

EFFECT  OF  INDIRECT  PULL  ON  A  LAPPED  JOINT 215 

EFFECT  OF  INDIRECT  PULL  ON  A  SINGLE  STRAPPED  JOINT 215 

CRACKS  IN  LAPPED  JOINT  DUE  TO  BENDING 216 

RIVETS  IN  PUNCHED  HOLES 217 

BUTT-STRAP  ON  A  STAYED  SHEET 224 

DOUBLE-RIVETED  BUTT-STRAP  OF  UNEQUAL  WIDTH  ON  A  STAYED  SHEET.  225 

DESIGN  FOR  A  TRIPLE-RIVETED  BUTT-STRAP 226 

STEAM-DOME 232 

STEAM-DRUM,  SINGLE  NOZZLE 233 

STEAM-DRUM,  DOUBLE  NOZZLE 234 

STEAM-DRUM,  PIPE  CONNECTION 234 

STANDARD  NOZZLES  OF  CAST-IRON  OR  CAST-STEEL 235 

ANGLE  BRACES  TO  SUPPORT  STOP-VALVE 236 

REINFORCING  STEAM-PIPES 240 

SLIP-JOINT  WITH  STUFFING-BOX  FOR  STEAM-PIPE 243 

PLAIN  FLANGE  FOR  COPPER  PIPE 244 

COLLAR  FLANGE  FOR  COPPER  PIPE 244 

PLAIN  FLANGE  WITH  SLEEVE  FOR  COPPER  PIPE 245 

COLLAR  FLANGE  WITH  EDGE  OF  COPPER  PIPE  TURNED  OVER 245 

FLANGE  FOR  IRON  OF  STEEL  PIPE 245 

FLANGES  WITH  TONGUE  AND  GROOVE 246 

FLANGES  CUT  AWAY  TO  FACILITATE  CALKING  EDGES  OF  PIPE 246 

FLANGES  WITH  RECESS  AND  PROJECTION 247 

FLANGES  WITH  FACES  GROUND  TO  FIT 247 

FEED-PIPE  ENTRANCE  WITH  DISTRIBUTING  END.  .  .  .  253 


xvi  LIST  OF  ILLUSTRATIONS 

PAGE 

FEED-PIPE  ENTRANCE.     (Two  views.) 254 

THE  METROPOLITAN  INJECTOR 255 

THE  GOUBERT  FEED-WATER  HEATER — CLOSED  TYPE 259 

HOPPES'  COMBINED  FEED-WATER  HEATER  AND  PURIFIER 261 

COCHRAN  FEED-WATER  HEATER — OPEN  TYPE 262 

GREEN  ECONOMIZER 263 

HOT-WELL  FILTER-BOX 264 

HOT-WELL  FILTER-BOX — DETAILS 265 

EDMISTON  TYPE  OF  FEED-WATER  FILTER 266 

RANKINE'S  PATENT  FEED-WATER  FILTER 266 

MUD-DRUM 267 

SURFACE  BLOW-OFF 268 

DEAD-WEIGHT  SAFETY-VALVE,  COBURN  TYPE 269 

VARIOUS  FORMS  OF  FUSIBLE  PLUGS 272 

WATER-GAUGE  AND  TRY-COCK  COLUMN 274 

GLASS  PROTECTOR  GUARDS  FOR  GLASS  TUBE  OF  WATER-COLUMN 275 

COMBINED  HIGH-  AND  LOW-WATER  ALARM  AND  WATER-COLUMN 276 

MANHOLE  AND  COVER  FOR  A  FLAT  SHEET 278 

MANHOLE  AND  COVER  FOR  A  CYLINDRICAL  SHELL 278 

SPLIT  BRIDGE  WITH  PASSAGE  TO  ADMIT  AIR.     (Two  views.) 279 

CAST-IRON  GRATE-BAR 280 

GRATE  BEARER  FOR  CORRUGATED  FURNACE 282 

PLAN  OF  HERRING-BONE  GRATE-BAR 282 

SHAKING-GRATE 283 

SECTION  OF  ASHCROFT  GRATE-BARS 283 

GRATE  FOR  BURNING  SAWDUST  OR  TAN-BARK 284 

DOWN-DRAFT  GRATE 284 

FIRE-DOOR  FOR  FURNACE    FLUE 287 

MORISON  FURNACE-DOOR  AND  FURNACE-FRONT 288 

KIELEY  DISCHARGE  TRAP 289 

BUNDY  RETURN  TRAP 290 

"POTTER"  MESH  SEPARATOR — LONGITUDINAL  SECTION 291 

"POTTER "  MESH  SEPARATOR — CROSS-SECTION 291 

STRATTON  STEAM-SEPARATOR 292 

SALT-WATER  EVAPORATOR 293 

THE  RONEY  MECHANICAL  STOKER 295 

THE  AMERICAN  MECHANICAL  STOKER 296 

THE  MURPHY  MECHANICAL  STOKER 297 

THE  MURPHY  MECHANICAL  STOKER.     Section 298 

BLOOMSBURG  JET  IN  STACK 302 

RING  JET  IN  STACK 303 

BEGGS'  ARGAND  STEAM-BLOWER 304 

BEGGS'  ARGAND  STEAM-BLOWER.     Section 305 

BEGGS'  ARGAND  BLOWER,  arranged  for  a  furnace-flue 306 

INDUCED  DRAFT — ELLIS  AND  EAVES'  SYSTEM 308 

BRICK  STACK.  .  .   331 


LlST  OF  ILLUSTRATIONS  xvil 

PAGE 

LADDER  FOR  BRICK  STACK 332 

BRICK  STACK,  cast-iron  cap  for 333 

SELF-SUPPORTING  STEEL  STACK 334 

PROF.  RINGELMANN'S  SMOKE-SCALES 339 

SUPERHEATER  ATTACHED  TO  A  BABCOCK  AND  WILCOX  BOILER 361 

SUPERHEATER  ATTACHED  TO  A  BABCOCK  AND  WILCOX  BOILER.    Section.  362 

FOSTER'S  SUPERHEATER  ATTACHED  TO  A  FIRE-TUBE  BOILER 362 

FOSTER'S  DETAIL  OF  RETURN  HEADER 363 

FOSTER'S  SUPERHEATER — DIRECT-FIRED  TYPE 364 

FOSTER'S  SUPERHEATER — SECTIONS  . . .. .   365 


STEAM-BOILERS 


CHAPTER  I 
PHYSICAL  PROPERTIES 

Solid  Bodies.  Fluid  Bodies.  Liquid  Bodies.  Gaseous  Bodies.  Perfect 
Gas.  Laws  of  Gases.  Heat.  Conduction.  Convection.  Radiation.  Me- 
chanical Equivalent  of  Heat.  Absolute  Zero.  Specific  Heat.  Latent  Heat. 
Total  Heat  of  Evaporation.  Weight  of  Water.  Boiling.  Relative  and 
Specific  Volumes  of  Steam.  Factor  of  Evaporation. 

THERE  are  two  principal  states  in  which  all  bodies  are  found, 
namely,  "Solids"  and  " Fluids."  Fluids  may  again  be  divided 
into  " Liquids"  and  " Gases." 

Solid  Bodies  may  be  defined  as  those  which  will  resist  a  longi- 
tudinal pressure,  no  matter  how  small  that  pressure  may  be,  with- 
out being  supported  by  a  lateral  pressure. 

Fluid  Bodies  may  be  defined  as  those  which  will  not  resist  such 
a  longitudinal  pressure. 

Liquid  Bodies  may  be  defined  as  those  which  will  only  partly 
fill  a  closed  vessel,  while  the  rest  of  the  vessel  may  be  either  empty 
or  contain  some  other  fluid. 

Gaseous  Bodies  may  be  defined  as  those  which  will  expand  and 
completely  fill  a  closed  vessel,  no  matter  how  small  a  portion  may 
be  introduced.  Gases  are  thus  distinguished  by  their  power  of 
indefinite  expansion. 

A  Perfect  Gas  may  be  described  as  one  which  obeys  exactly  the 
laws  of  Mariotte  and  of  Gay-Lussac.  Such  a  perfect  gas  is  now 
known  to  be  ideal,  and  the  so-called  permanent  gases  only  approx- 
imate in  their  action  to  these  laws  in  accordance  with  their  degree 
of  perfection. 


2  STEAM-BOILERS 

Laws  of  Gases.  First  Law  (Mariotte  or  Boyle):  "At  constant 
temperature,  the  volume  of  a  portion  of  gas  varies  inversely  as  the 
pressure."  That  is,  pv  =  constant. 

Second  Law  (Gay-Lussac,  Charles,  or  Dalton):  "At  constant 
pressure,  the  volume  of  a  portion  of  gas  varies  directly  as  the  abso- 
lute temperature."  That  is,  v  =  const  ant  Xr- 

Heat.  There  are  many  words,  such  as  "hot,"  "warm,"  "tepid," 
"cool,"  "cold,"  which  are  used  to  denote  different  sensations  that 
indicate  a  corresponding  condition  of  the  object  with  respect  to 
the  heat  which  it  is  said  to  contain.  These  conditions  or  series  of 
states  are  called  "Temperatures,"  and  from  the  facts  as  found  in 
nature  it  must  be  admitted  that  there  exists  an  infinite  number 
of  these  intermediate  states  or  temperatures. 

The  temperature  of  a  body,  therefore,  indicates  how  hot  the 
substance  is.  These  temperatures  are  accompanied  in  each  body 
by  certain  conditions  as  to  the  relations  between  density  and  elas- 
ticity. In  general,  the  hotter  the  body,  the  less  is  its  elasticity  of 
figure  and  the  greater  is  its  elasticity  of  volume. 

Heat  may  be  considered  as  a  "mode  of  motion,"  and  is  gener- 
ally recognized  to  be  a  vibratory  motion  of  the  particles  composing 
any  body. 

Heat  is  transferable  from  one  body  to  another,  that  is,  one  body 
can  heat  another  by  becoming  less  hot  itself.  This  transfer  of  heat 
between  two  bodies  tends  to  bring  them  to  a  state  called  "uniform" 
or  "equal"  temperature.  At  uniform  temperature  this  transfer 
of  heat  ceases. 

Heat  is  transferred  from  a  warmer  body  to  a  colder  body  by 
one  of  three  processes,  namely,  "Conduction,"  "Convection"  and 
"Radiation." 

Conduction  is  the  transference  of  heat  between  two  contiguous 
portions  of  matter  at  different  temperatures.  Convection  is  the 
distribution  of  heat  by  a  movement  of  a  portion  of  a  fluid  within 
its  own  mass.  Such  a  movement  is  called  a  convection  current. 
Radiation  is  the  transference  of  heat  from  one  body  to  another  at 
a  distance,  through  an  intervening  transparent  medium. 

Heat  is  one  of  the  forms  of  energy,  since  it  may  be  transformed 
into  mechanical  work. 

As  the  condition  of  heat  is  a  condition  of  energy,  and  is  capable 
of  effecting  changes,  it  may  be  indirectly  measured,  so  as  to  be 


PHYSICAL  PROPERTIES  3 

expressed  as  a  quantity  by  means  of  one  or  more  of  the  directly 
measurable  effects  which  it  produces. 

When  the  condition  of  heat  is  thus  expressed  as  a  quantity,  it 
is  subject,  like  all  other  forms  of  energy,  to  a  law  of  conservation. 

Since  the  properties  of  all  substances  vary  with  their  tempera- 
tures, it  has  become  customary  to  make  use  of  two  of  these  varia- 
tions to  indicate  particular  temperatures  as  points  of  reference. 
These  two  variations  were  selected  because  they  were  abrupt  and 
well  defined,  and  are : 

First.  The  temperature  at  which  ice  melts  under  one  atmos- 
phere of  pressure,  equivalent  to  14.7  pounds  per  square  inch  or  u 
barometric  height  of  29.95  inches.  As  this  temperature  varies  but 
slightly  with  changes  of  pressure,  it  can  be  easily  reproduced  under 
ordinary  conditions. 

Second.  The  temperature  of  steam  generated  from  water  when 
boiled  under  one  atmosphere  of  pressure. 

Occasional  use  is  made  of  other  changes  of  state,  which  take 
place  at  temperatures  more  or  less  well  defined,  such  as  the  melting- 
points  of  certain  metals  and  alloys. 

Ordinary  temperatures  are  recorded  from  the  reading  of  a  mer- 
curial thermometer.*  For  higher  temperatures  use  is  made  of  the 
air-thermometer  or  some  form  of  pyrometer. 

Heat  and  work  are  mutually  convertible  in  a  fixed  ratio,  known 
as  the  " Mechanical  Equivalent  of  Heat."  The  relationship  exist- 
ing between  heat  and  work,  was  demonstrated  by  various  experi- 
ments, the  most  noted  being  those  of  Benjamin  Thompson,  better 
known  as  Count  Rumford  (1753-1814),  Sir  Humphry  Davy  (1778- 
1829),  Sadi  Carnot  (1796-1832)  and  Henry  A.  Rowland  (1848- 
1901).  In  1842,  Dr.  Mayer,  of  Heilbronn,  is  said  to  have  first  intro- 
duced the  expression  "  Mechanical  Equivalent  of  Heat,"  and  in 
the  year  following  Dr.  Joule,  of  Manchester,  measured  this  equiva- 
lent. The  value  placed  by  Joule  was  772  foot-pounds  of  work  as 
equivalent  to  one  British  thermal  unit.  This  result  is  still  in  use, 


*  In  order  accurately  to  read  a  mercurial  thermometer,  when  the  scale 
is  not  on  the  same  plane  with  the  column  of  mercury,  it  will  be  found  con- 
venient to  hold  a  small  looking-glass  behind  the  column  of  mercury;  then, 
when  the  eye  is  so  reflected  that  the  centre  of  the  pupil  is  coincident  with 
the  top  of  the  mercury,  the  eye  will  be  at  right  angles  to  the  mercury  and 
also  to  the  scale. 


4  STEAM-BOILERS 

although  later  experiments  show  that  778  foot-pounds  is  nearer 
the  true  figure.  This  latter  result  will  be  used  in  this  work  except 
where  otherwise  stated. 

The  British  thermal  unit  is  the  quantity  of  heat  required  to 
raise  one  pound  of  pure  water  at  its  maximum  density  one  degree 
Fahrenheit.  The  temperature  of  water  at  maximum  density  is 
very  nearly  39.2°  F. 

The  Absolute  Zero.  In  order  to  simplify  calculations  with  re- 
spect to  the  action  of  perfect  gases,  all  the  formulae  are  based  on 
a  scale  of  absolute  temperatures.  These  absolute  temperatures 
express  the  heat  of  a  body  on  a  scale  beginning  at  a  point  known 
as  the  "absolute  zero." 

The  absolute  zero  is  a  theoretical  point  on  this  temperature 
scale  that  is  fixed  by  assuming  that  the  law  of  gases  as  deter- 
mined by  experiment  remains  constant  throughout  the  whole 
range  of  temperatures. 

It  may  be  said  to  be  the  temperature  point  corresponcjing  to 
the  disappearance  of  gaseous  elasticity,  or  the  point  at  which  the 
expression  pv  for  a  perfect  gas  becomes  zero. 

When  a  portion  of  dry  air  is  heated  from  the  freezing-point  of 
water  (32°  F.)  to  the  boiling-point  (212°  F.),  that  is,  its  tempera- 
ture has  been  raised  through  180°  F.,  it  will  expand  to  1.365  of  its 
original  volume.  Therefore,  when  the  gas  has  been  heated  through 
493.2°,  it  will  expand  to  twice  its  original  volume.  If,  therefore, 
the  same  law  holds  true  for  cooling,  and  the  temperature  be  lowered 
493.2°  from  the  freezing-point  (32°),  the  volume  of  the  gas  will  be 
reduced  to  zero.  But  the  law  of  expansion  and  contraction  of  the 
so-called  permanent  gases  varies  appreciably,  so  that  there  is  a 
slight  difference  in  the  position  of  the  absolute  zero  according  to 
the  gas  under  experiment. 

The  assumed  zero-point  is  the  absolute  zero  of  the  scale,  and  is 
approximately  493.2°- 32°- 461.2°  F.  below  the  ordinary  zero 
Fahrenheit. 

This  is  shown  graphically  in  Fig.  1. 

The  Specific  Heat  of  a  substance  is  its  capacity  for  heat.  As 
usually  expressed,  it  is  the  quantity  of  heat,  stated  in  thermal  units, 
which  must  be  transferred  to  or  taken  from  a  unit  of  weight  of  a 
given  substance,  in  order  to  raise  or  lower  its  temperature  one 
degree  at  a  certain  specific  temperature. 


PHYSICAL   PROPERTIES 


Specific  heats  are  not  constant  for  solids  and  liquids.  They 
become  greater  as  the  temperature  increases;  and,  further,  the 
greater  the  coefficient  of  expansion  of  a  substance,  the  greater 
will  be  the  increase  in  the  specific  heat. 

The  specific  heats  of  the  perfect  gases  remain  constant,  as  far 
as  temperature  or  density  is  concerned,  so  that  equal  increments 

FAHR.         ABSOLUTE 
986.4° 


493.2, 
61.2 


VOLUMES  OF  A  GAS 


THERMOMETERS 

FIG.  1.— The  Absolute  Zero. 

of  temperature  correspond  to  equal  quantities  of  heat.  Hence 
we  may  infer  that  at  the  absolute  zero  gaseous  bodies  become 
entirely  destitute  of  the  condition  called  "heat." 

It  was  shown  by  LaPlace  that  there  were  two  kinds  of  specific 
heats  for  gases,  one  corresponding  to  constant  pressure  and  one  to 
constant  volume. 

When  a  gas  is  heated  at  constant  pressure,  the  heat  taken  in 


STEAM-BOILERS 


is  Kp(r2—  TJ)  and  the  work  done  is  P(V2—V1)  =  c(r2—r1). 
difference  is  the  amount  of  increase  of  internal  energy,  or 


The 


When  a  gas  is  heated  at  constant  volume,  no  external  work  is 
done.  Therefore  the  specific  heat  at  constant  volume  is  always 
less  than  that  at  constant  pressure.  In  this  case  the  heat  taken 
in  is  Kv(r2—  TJ),  which  represents  the  increase  of  internal  energy. 

Equating  these  values, 


The  ratio  of  j/-  is  usually  denoted  by  ?-. 
Kv 

TABLE  I 

THE    SPECIFIC    HEAT    OF    A    FEW    SUBSTANCES 


Substance. 

Weight  in  Pounds  of 
1  Cu.  Ft.  under 
1  Atmosphere 

Specific  Heat. 

Kv. 
Constant 
Volume. 

KP. 
Constant 
Pressure. 

at  32°  F. 

at  60°  F. 

Water  at  maximum  density  
Sea-water 

62.425 
64.090 
57  500 

62.367 

1.000 

Ice 

0.5 
0.393 
0.1697 
0.1542 
2.4177 
0.1729 
0.370 
0  .  1733 
0.1692 

04 
0.508 
0.2375 
0.2175 
3.4090 
0.2438 
0.480 
0.2426 
0.2169 

Anhydrous  ammonia 

0.0482 
0.0807 
0.0892 
0.0056 
0.0782 
0.0502 
0.0782 
0.1227 

Air                 

0.0764 
0.0844 
0.0053 
0.0740 

6.0740 
0.1161 

Oxvsren 

Hvdroffen 

"^itrosren 

Gaseous  steam 

Carbon  monoxide  ffas 

Carbon  dioxide  seas  . 

Note. — Authorities  differ  as  to  these  figures. 

From  the  definition,  the  specific  heat  of  water  at  its  maximum 
density  is  unity.  For  other  densities  within  the  commercial  range 
the  difference  is  so  slight  that  for  all  practical  calculations  it  may 
be  taken  as  constant. 

Latent  Heat.  When  a  body  changes  its  state  a  certain  amount 
of  heat  is  either  taken  in  or  given  out.  This  exchange  of  heat  is 
necessary  in  order  to  effect  such  change  of  state,  and  under  like 
circumstances  is  always  the  same  in  amount.  Thus,  suppose  a 
given  amount  of  water  is  at  60°  F.  with  a  normal  barometric  pres- 
sure. Heat  the  water  and  its  temperature  will  rise  until  it  has 


PHYSICAL  PROPERTIES 


become  212°  F.  At  this  point  increase  of  temperature  will  cease, 
but  the  water  will  continue  to  absorb  heat  and  commence  to  gen- 
erate steam,  which  process  will  continue  until  all  the  water  has 
been  vaporized.  During  the  change  of  state  each  pound  of  water 
will  absorb  965.7  B.  T.  U.  This  disappearance  of  heat  represents 
work  done  on  the  particles  composing  the  water  as  they  are  moved 
farther  away  from  each  other  against  the  molecular  attraction. 

Had  the  pressure  been  greater  than  one  atmosphere,  then  the 
water  would  not  have  boiled  until  the  temperature  had  been  raised 
more  than  212°  F.,  and  also  less  than  965.7  B.  T.  U.  would  have 
been  required  per  pound  to  effect  the  change  of  state.  The  boiling- 
temperatures  and  the  heat  absorbed  to  change  the  state  are  con- 
stant for  their  corresponding  pressures. 

The  converse  of  the  above  is  also  true. 

The  heat  thus  absorbed  or  given  out  is  called  the  "  Latent 
Heat/'  in  order  to  distinguish  it  from  the  "  Sensible  Heat/'  which 
is  the  heat  necessary  to  change  a  body's  temperature. 

Latent  Heat  may  be  defined  as  the  quantity  of  heat  which  must 
be  communicated  to  or  taken  from  a  body  in  a  given  state  in  order 
to  convert  it  into  another  state  without  changing  its  temperature. 

The  most  important  cases  are: 

1.  The  latent  heat  of  fusion,  or  the  conversion  of  solids  into 
liquids. 

The  following  table  gives  the  latent  heat  of  fusion  of  a  few  sub- 
stances, expressed  in  British  thermal  units  per  pound,  under  one 
atmosphere  of  pressure.  These  quantities  -change  but  little  with 
variations  of  pressure. 

TABLE  II 

LATENT    HEAT    OF    FUSION    OF    A    FEW    SUBSTANCES 


Ice 144.0 

Cast  iron 233 . 0 

Zinc..  50.6 


Tin 25.6 

Bismuth 22.7 

Lead..  9.6 


2.  The  latent  heat  of  evaporation,  or  the  conversion  of  liquids 
into  the  gaseous  state. 

The  following  is  a  table  of  the  latent  heat  of  evaporation  of  a 
few  substances  when  the  pressure  of  the  vapor  is  at  one  atmosphere, 
expressed  in  British  thermal  units.  This  latent  heat  decreases 
very  perceptibly  as  the  pressure  increases. 


STEAM-BOILERS 
TABLE  III 

LATENT    HEAT    OF    EVAPORATION    OF    A    FEW    SUBSTANCES 


Substance. 

Boiling-point. 

Latent  Heat. 

Water  

212°      F. 

965.7 

Anhydrous  ammonia 

-28  5°  F 

572  7 

Alcohol  .... 

172  2°  F 

364  3 

Ether      . 

95°      F 

162  8 

3.  The  latent  heat  of  expansion,  or  the  heat  which  disappears 
in  causing  the  volume  of  a  body  to  increase  under  a  constant  pres- 
sure. 

4.  There  are  many  chemical  changes  during  which  heat  is  gen- 
erated or  disappears. 

For  all  work  in  connection  with  the  design  and  management 
of  steam-boilers  the  latent  heat  of  evaporation  is  by  far  the  most 
important. 

As  has  already  been  stated,  this  latent  heat  varies  in  amount 
with  the  pressure  under  which  the  vaporization  takes  place,  but 
is  constant  for  the  same  pressure.  The  amount  of  latent  heat  re- 
quired decreases  as  the  pressure  increases. 

Furthermore,  the  same  quantity  of  latent  heat  which  was 
absorbed  in  the  first  place  as  latent  heat  of  evaporation  must  be 
again  given  out  by  the  body  when  it  changes  its  state  back  from 
the  vapor  to  the  liquid;  and  this  heat  must  be  transferred  to  some 
other  body  and  carried  away,  in  order  that  this  process  of  conden- 
sation may  go  on. 

The  following  empirical  formula  represents  with  great  accu- 
racy the  experiments  of  M.  Regnault  on  the  latent  heat  of  evapo- 
ration of  water.  The  latent  heat  of  one  pound  of  water  in  British 
thermal  units  is  denoted  by  I,  and  any  temperature  Fahrenheit 
by  T;  then 

1=  1091.7-  0.695  { T°-  32°  |  -  0.000,000,103  { T°-  39.1°! 3. 

As  this  formula  is  rather  complicated  for  easy  use,  it  is  sufficient 
for  all  practical  work,  when  a  steam-table  is  not  at  hand,  to  use  the 
following  form,  thus : 

1=  1092-  0.7  { T°-  32°  1=966-  0.7  \T°-  212°  j. 


PHYSICAL   PROPERTIES  9 

Total  Heat  of  Evaporation.  The  "  total  heat  of  evaporation  " 
is  a  conventional  phrase,  used  to  denote  the  heat  that  is  taken  in 
by  a  substance  when  it  is  raised  from  some  lower  temperature  and 
evaporated  at  a  higher  temperature.  The  heat  necessary  to  raise 
the  temperature  from  the  lower  temperature  to  that  of  evaporation 
is  known  as  the  "sensible  heat." 

The  total  heat  of  evaporation  is  then  the  sum  of  the  sensible 
and  latent  heats. 

M.  Regnault  found  by  experiment  that  the  total  heat  in- 
creased for  water  at  a  uniform  rate  as  the  temperature  of  evapora- 
tion rises.  He  proposed  the  following  empirical  formula  for  calcu- 
lating the  total  heat  of  evaporation  for  water,  thus: 

h=  1091.7+  0.305  { T°-  32°} . 

In  this  expression  h  denotes  the  total  heat  of  one  pound  of  water, 
raised  from  the  freezing-point  to  any  temperature  7"°  F. 

As  in  most  cases  the  lower  fixed  temperature  is  above  that  of 
melting  ice,  the  total  heat  of  evaporation  will  then  be  less  than  that 
given  by  the  formula,  by  the  amount  of  heat  contained  between 
32°  F.  and  such  initial  temperature. 

Without  causing  an  error  of  any  practical  moment,  small  frac- 
tions may  be  neglected,  and  also  the  specific  heat  of  water  may  be 
taken  as  constant,  at  unity.  Then,  for  all  commercial  purposes, 
whenever  it  be  required  to  determine  the  total  heat  of  evaporation 
from  any  temperature  T2°  to  another  at  7\°,  Regnault's  formula 
may  be  simplified  as  follows : 

h^  =  1092+  0.3  j  T°-  32° }  -  j  772°-  32° } . 

Weight  of  Water.  Rankine's  empirical  formula  to  calculate 
the  weight  of  water  at  different  temperatures,  will  often  be  found 
convenient  when  a  water-table  is  not  at  hand. 

The  weight  of  one  cubic  foot  of  water  at  any  temperature, 
T°j  will  be  very  nearly  equivalent  to  the  following  expression: 

2X62.425 
_r_  500' 
500 +~T 

r  denoting  absolute  temperature  corresponding  to  T°  F. 


10  STEAM-BOILERS 

Boiling.  On  the  application  of  heat  the  temperature  of  water 
increases  until  it  reaches  the  "  boiling-point."  The  water  will  con- 
tinue to  absorb  heat,  although  its  temperature  will  remain  constant. 
When  sufficient  latent  heat  has  been  absorbed  in  order  to  effect  a 
change  of  state,  the  water  will  begin  to  boil.  The  temperature  of 
the  boiling-point  increases  with  the  pressure,  but  is  always  con- 
stant for  its  corresponding  pressure. 

Water  does  not  boil  from  the  surface,  but  bubbles  of  steam  form 
throughout  the  mass  and  rise  to  the  surface.  This  action  is  very 
violent  in  steam-boilers,  and  bubbles  of  steam  rise  so  rapidly  as 
often  to  carry  considerable  water  in  mechanical  suspension  into  the 
steam.  This  action  is  called  "priming,"  and  it  occurs  most  fre- 
quently in  poorly  designed  boilers  and  in  those  that  are  forced 
beyond  their  capacity.  It  is  also  encouraged  by  use  of  dirty  or 
greasy  water. 

The  action  of  boiling  is  resisted  when  made  to  take  place  in  glass 
vessels  and  in  those  formed  of  materials  which  attract  water.  In 
such  vessels  ebullition  is  not  continuous.  Ebullition,  therefore, 
is  not  truly  represented  in  small  glass  models,  although  many  have 
been  used  by  selling  agents  to  illustrate  some  so-called  faulty  action 
in  other  makers'  boilers. 

Salt  water  or  brine  also  resists  ebullition,  and  the  boiling-point 
for  salt  water  is  higher  than  that  for  fresh  water  under  the  same 
pressure. 

The  boiling-point  for  saturated  brine  under  one  atmosphere 
is  226°  F.  For  each  3^  part  by  weight  of  salt  which  the  water  con- 
tains the  boiling-point  is  raised  about  1.2°  F. 

Average  sea-water  contains  about  -fa  of  salt,  but  it  varies  some- 
what in  different  parts  of  the  globe.  It  is  usual  to  speak  of  the 
quantity  of  salt  contained  as  being  in  32ds,  although  the  quantity 
is  often  expressed  as  so  many  ounces  to  the  gallon. 

When  sea-water  is  used  in  marine  boilers  the  brine  should  not 
be  allowed  to  get  stronger  than  •£%  or  -fa,  and  preference  should  be 
given  to  the  lesser  limit.  Saturated  brine  contains  about  30  per 
cent  of  salt,  or  nearly  |f. 

The  strength  of  the  solution  in  the  boiler  should  be  tested  at 
frequent  intervals  by  blowing  out  a  little  water  into  a  pail,  and 
measuring  its  strength  by  a  hydrometer  or  salinometer,  the  zero 
of  which  instrument  is  the  floating  mark  in  fresh  water. 


PHYSICAL   PROPERTIES  11 

Salinometers  may  be  bought,  but  in  case  of  breakage  can  easily 
be  replaced  temporarily  by  using  a  vial  weighted  with  shot  so  as 
to  make  it  float  in  an  upright  position.  Place  the  vial  in  pure 
water  and  scratch  a  mark  for  the  zero-point.  Then  place  in  satu- 
rated brine  and  mark  again.  Divide  the  space  between  the  marks 
into  ten  equal  divisions,  and  each  will  represent  approximately 
-g1^  of  salt. 

Relative  and  Specific  Volumes  of  Steam.  The  volume  of  any 
given  portion  of  steam,  compared  to  that  of  the  water  from  which 
it  was  evaporated,  is  called  the  relative  volume  of  steam  for  that 
corresponding  pressure.  The  specific  volume  is  the  volume  of 
steam  generated  from  one  pound  of  water. 

Under  one  atmosphere  or  14.7  pounds  per  square  inch  absolute, 
one  cubic  foot  of  water  will  occupy  about  1642  cubic  feet  when  con- 
verted into  steam.  Under  ten  atmospheres  or  147  pounds,  the 
steam  would  occupy  nearly  189.7  cubic  feet.  From  these  two 
examples  can  be  seen  what  an  enormous  expansive  force  there  is 
in  steam. 

Steam-tables  give  the  corresponding  absolute  pressures,  tem- 
peratures, total  heats  of  evaporation,  weights  and  volumes. 

Factor  of  Evaporation.  The  value  of  any  fuel  as  a  heat-gen- 
erating agent  is  generally  expressed  in  the  ''weight  of  water  that 
it  will  evaporate  per  pound."  But  the  temperature  of  the  feed- 
water  and  the  temperature  or  pressure  at  which  evaporation  takes 
place  will  greatly  affect  the  quantity  evaporated  and  therefore 
the  apparent  value  of  the  fuel.  In  order  to  make  all  results  com- 
parable, it  is  customary  to  reduce  the  actual  amount  of  water 
evaporated  to  that  which  would  have  been  evaporated  had  the 
feed-water  been  supplied  at  a  temperature  of  212°  and  the  evapora- 
tion taken  place  at  212°,  that  is,  under  one  atmosphere  of  pressure. 

This  result  is  called  "the  equivalent  evaporation  from  and  at 
21%°"  and  the  weight  of  water  so  found  per  pound  of  fuel  is  said 
to  be  "the  evaporative  power  of  the  fuel." 

To  find  this  quantity,  it  is  only  necessary  to  determine  the 
total  heat  of  evaporation  under  the  actual  conditions  by  means  of 
the  formula,  or  from  the  steam-tables,  and  divide  by  966,  the 
latent  heat  of  evaporation  of  water  at  212°.  The  quotient  will  be 
a  multiplier,  by  which  the  actual  evaporation  must  be  multiplied 
in  order  to  get  the  equivalent  quantity  from  and  at  212°.  This 


12 


STEAM-BOILEKS 


multiplier  is  called  the  "factor  of  evaporation"      A    convenient 
expression  for  determining  this  factor  of  evaporation  is: 


Factor  of  Evaporation  =  1  + 


0.317V3-  212°}  +{212°-T, 
966 


in  which  T°  denotes  the  temperature  of  the  steam  and  T2Q  that 
of  the  feed-water. 

TABLE  IV 

ABSOLUTE    PRESSURES,    BOILING-POINTS    AND    FACTORS    OF    EVAPORATION 


Factors  of  Evaporation, 

Pressures, 

Feed-water  Temperatures. 

Absolute, 

Boiling-point. 

per 

Square  Inch. 

50°. 

104°. 

14.7 

212°      F. 

1.169 

.113 

52.5 

284°      F. 

1.190 

.136 

90.0 

320°      F. 

.203 

.147 

115.3 

338°      F. 

.208 

.152 

146.0 

356C      F. 

.214 

.158 

160.0 

363  .  4°  F. 

.216 

1.160 

200.0 

381.7°  F. 

.222 

1.166 

336.0 

428°      F. 

.235 

1.179 

Example.     Assume  the  following  data: 

A  boiler  evaporates  per  hour,  actual  ......  =  12,000  Ibs.  of  water 

Coal  burnt  per  hour  .....................  =   1,400  Ibs. 

Actual  water  evaporated  per  pound  of  coal 

12000 
per   hour=  ......................  =   8.57  Ibs. 

14UU 

Temperature  of  feed-water,  T°  .............  =  104° 

Temperature  of  steam  at  120  Ibs.  gauge  pres- 

sure, T°  .............................  =350° 

Then 


Factor   of    evaporation 


h0  ,  =  1115.4 
=     1ggg~~~       s  1.154 


and  equivalent  evaporation  from  and  at  212° 

is  8.57X  1.154.  .  .............  =9.89  Ibs. 


CHAPTER  II 
COMBUSTION 

General  Conditions.  Definition.  Smoke.  Coal-Gas.  Marsh-Gas.  Ole- 
fiant  Gas.  Air.  Temperatures  of  Ignition.  Laws  of  Avogadro.  Require- 
ments for  Perfect  Combustion.  Products  of  Combustion.  Composition  of 
Gases  from  Combustion.  Refuse.  Loss  of  Unburned  Coal  in  Ash-pit.  Quan- 
tity of  Air  Required.  Methods  of  Firing.  Thickness  of  Fire.  Heat  of  Com- 
bustion. Heating  Power  of  a  Fuel. 

As  the  power  developed  by  the  steam-engine  is  derived  from 
the  form  of  energy  called  "Heat,"  and  as  this  heat  is  obtained  by 
the  combustion  of  a  fuel,  it  is  essential  that  the  principles  involved 
and  the  natural  laws  relating  thereto  be  clearly  understood.  Fur- 
thermore, since  the  engineer  designs  the  engine  to  perform  a  certain 
amount  of  work  at  a  high  economy,  there  should  be  no  deficiency 
of  steam  or  want  of  heat,  or  no  excess  of  steam  or  too  great  an 
expediture  of  fuel.  Unfortunately,  many  steam  plants  have  given 
poor  satisfaction,  simply  from  want  of  care  in  the  design  of  the 
furnace. 

By  combustion  is  meant  "chemical  union,"  and  in  general  this 
union  is  productive  of  heat. 

It  is  a  union  between  a  combustible  or  fuel  and  a  supporter  of 
combustion.  This  supporter  of  combustion,  within  the  limits  of 
this  work,  is  the  oxygen  contained  in  the  atmosphere. 

The  principal  fuels  are  coal,  wood,  gas  and  oil. 

The  chief  constituents  of  these  fuels  are  carbon  and  hydrogen, 
but  their  characteristics  and  modes  of  entering  into  combustion 
are  very  different. 

The  carbon  is  reduced  to  carbon  dioxide,*  the  hydrogen  to  water 
or  steam,  sulphur  to  sulphurous  or  sulphuric  acid,  and  any  other 
elements,  commonly  called  impurities,  to  their  respective  oxides. 

*  Carbon  dioxide  is  also  known  as  carbon  anhydride,  and  frequently, 
although  erroneously,  as  carbonic  acid. 

13 


14  STEAM-BOILERS 

A  fresh  charge  of  coal  when  thrown  on  a  fire  in  an  active  state 
becomes  a  great  absorbent  of  heat.  This  apparent  loss  of  heat  is 
utilized  in  volatilizing  the  bituminous  portion,  and  is  a  very  cooling 
process,  due  to  the  change  of  sensible  into  latent  heat.  While  this 
generation  of  the  gases  is  taking  place  the  carbonaceous  part  re- 
mains black  or  at  a  low  temperature,  awaiting  the  proper  time  for 
it  to  burn. 

If  the  bituminous  portion  be  not  utilized  in  the  gaseous  state 
for  the  production  of  heat,  it  becomes  a  total  loss  and  were  better 
absent,  as  in  that  case  all  the  latent  heat  would  have  been 
available.  It  is  due  to  this  fact  that  the  bituminous  coals  do  not 
give  such  an  intense  heat  as  the  anthracites. 

The  above  reasoning  will  explain  why  firemen  throw  fresh  coal 
into  a  furnace  in  order  to  temporarily  cool  it,  as,  for  instance,  when 
the  engine  suddenly  stops,  or  for  some  other  cause  there  is  a  less- 
ened demand  for  steam. 

In  order  to  effect  complete  combustion,  the  particles  composing 
the  gaseous  and  carbonaceous  portions  of  the  fuel  must  be  brought 
into  contact  with  the  oxygen  of  the  air  supplied.  The  great  diffi- 
culty is  the  proper  mixing  of  the  gases.  If  all  the  carbon  is  burned 
to  carbon  dioxide,  there  must  be  an  excess  of  air  passing  through 
the  furnace.  If  all  the  carbon  is  not  burned  in  the  short  time 
allowed  with  a  powerful  draft,  due  to  a  lack  of  mixture  or  to  a 
deficiency  of  air,  the  carbon  is  wasted  as  carbon  monoxide  or  half- 
burned  carbon,  or  in  vaporized  carbon  which  is  commonly  called 
smoke. 

If  once  smoke  be  produced,  it  will  be  a  difficult  matter  to  con- 
sume it.  It  is  not  so  difficult  to  burn  coal  without  producing 
smoke  by  a  proper  admixture  of  air,  introduced  in  suitable  pro- 
portions and  in  a  manner  to  bring  the  particles  of  carbon  in  contact 
with  the  oxygen  when  at  high  temperature.  This  is  the  real  result 
that  should  be  accomplished.  For  ordinary  practice  it  is  then  a 
misapplication  of  words  to  say  "how  smoke  from  coals  may  be 
burned."  The  more  correct  expression  would  be  " burning  coals 
without  producing  smoke." 

No  definite  rule  can  be  laid  down  for  the  admission  of  air  so  as 
to  burn  all  kinds  of  coal  without  producing  smoke,  as  each  variety 
of  coal  has  its  peculiar  qualities  and  as  so  much  depends  on  the 
design  of  furnace,  grate,  nearness  of  heating  surfaces  and  strength 


COMBUSTION  15 

of  draft.  What  is  desired  is  that  the  air  shall  be  thoroughly 
mixed  with  the  particles  of  fuel  before  the  latter  are  too  much 
cooled  by  contact  with  the  boiler  surfaces.  For  some  bituminous 
coals,  a  supply  of  air  admitted  above  the  grate  and  also  behind 
the  bridge  wall  is  often  most  desirable  and  necessary. 

In  the  intense  heat  of  a  fiercely  burning  fire  the  bituminous 
coals  are  vaporized  with  such  great  rapidity,  that  it  is  practically 
impossible  to  burn  all  the  gaseous  portion  before  it  flies  to  the 
chimney  and  passes  beyond  the  reach  of  combustion.  However, 
much  may  be  accomplished  by  a  regular  firing  of  small  quantities 
at  a  time  in  order  to  reduce  the  smoke  nuisance.  Some  of  the 
mechanical  systems  for  firing  have  been  very  successful  in  this 
regard. 

Of  all  the  different  kinds  of  furnaces  designed  for  various  pur- 
poses, the  most  persistent  smoker  is  that  of  the  steam-boiler.  The 
reason  is  obvious,  as  there  are  no  hot  walls  to  radiate  back  the  heat 
and  thus  aid  combustion. 

In  some  designs  of  boilers  the  furnace  is  enclosed  in  a  fire-brick 
combustion-chamber,  and  the  products  are  not  admitted  to  the 
heating  surfaces  until  after  combustion  has  become  more  or  less 
perfect.  This  arrangement  has  met  with  success  in  many  instances, 
and  could  be  carried  much  farther  than  it  is. 

The  object  of  the  boiler  is  to  rob  the  fuel  of  its  heat  as  quickly 
as  possible;  therefore  every  particle  of  gas  and  carbon  that  comes 
unburned  into  contact  with  the  water  surfaces  is  cooled  below  the 
temperature  of  perfect  union,  and  must  be  drawn  into  the  stack 
in  its  unburned  condition,  surplus  of  air  or  not,  and  must  add  to 
the  volume  of  smoke. 

Many  smoke-consuming  devices  are  advertised  which  claim  a 
saving  in  fuel  of  from  ten  to  twenty-five  per  cent.  Authorities 
agree  that  the  extreme  loss  due  to  smoke  is  less  than  five  per  cent; 
therefore  if  the  advertised  devices  do  save  as  much  as  they  claim  - 
they  are  misnamed.  Instead  of  being  "  smoke-consumers/7  they 
should  be  called  "heat-savers."  * 

When  heat  is  applied  to  coal,  the  resulting  combustion  is 
effected  as  follows:  first,  the  absorption  of  heat;  second,  the 

*  The  engineer  should  be  very  careful  not  to  place  too  much  value  on 
advertising  matter,  catalogue  statements  and  the  like,  as  they  ars  apt  to 
be  misleading. 


16  STEAM-BOILERS 

vaporization  of  the  bituminous  or  hydrocarbon  portion  and  its 
combustion;  and  third,  the  combustion  of  the  solid  or  carbonaceous 
part.  These  actions  are  entirely  separate  and  distinct,  and  must 
take  place  in  the  order  as  given.  The  hydrocarbon  or  bituminous 
portion  consists  of  marsh-gas,  olefiant  gas,  tar,  pitch,  naphtha,  etc. 

The  flame  is  derived  from  the  gaseous  portion,  and  this  explains 
why  the  soft  or  bituminous  coals  burn  with  more  flame  than  the 
anthracites. 

Coal-gas,  taken  by  itself,  is  not  inflammable,  as  a  lighted  taper 
placed  in  a  jar  of  coal-gas  will  be  extinguished.  In  order  to  con- 
sume it  oxygen  must  be  supplied,  that  is,  the  gas  must  be  mixed 
with  air.  When  this  is  done  the  gas  will  be  consumed  instantly, 
provided  the  proper  temperature  be  present. 

When  a  charge  of  fresh  coal  is  thrown  on  a  fire  we  cannot  con- 
trol the  amount  of  gas  that  may  be  generated,  but  we  can  control 
the  supply  of  air.  Therefore  it  is  essential,  when  soft  coals  are 
to  be  burned,  that  a  certain  amount  of  air  be  admitted  in  addition 
to  the  regular  supply  through  the  grate,  during  the  periods  of 
evolution  of  the  gases.  This  can  be  accomplished  by  permitting 
air  to  enter  above  the  grate,  or  directly  into  the  combustion-cham- 
ber behind  the  bridge  wall,  or  both.  The  quantity  admitted  should 
bear  some  suitable  relation  to  the  percentage  of  the  hydrocarbons 
contained  in  the  fuel.  It  is  best  in  all  cases  to  provide  ample  pas- 
sages for  the  air,  and  then  to  admit  the  proper  quantity  as  deter- 
mined by  trial  and  observation  of  the  smoke  produced. 

In  order  to  burn  coal  economically,  it  has  been  found  necessary 
that  an  excess  of  air  should  be  allowed  to  enter  the  furnace.  If 
only  the  theoretical  quantity  be  supplied,  a  large  proportion  of  the 
carbon  will  either  not  be  consumed  or  be  only  half  burned  to 
carbon  monoxide  (CO). 

On  the  other  hand,  too  great  an  excess,  as  well  as  a  deficiency 
of  air,  is  a  detriment  to  the  economical  working  of  the  furnace. 

Much  depends  upon  the  design,  especially  with  soft  coals,  for 
the  requisite  quantity  may  be  supplied  in  a  manner  as  not  to  be 
available ;  that  is,  the  particles  of  oxygen  may  not  come  into  con- 
tact with  particles  of  carbon.  In  short,  the  air  and  particles  of 
fuel  may  not  mix,  but  rush  to  the  chimney  in  "  stream-lines." 

Coal-gas  is  composed  of  hydrogen  and  carbon,  and  the  prin- 
cipal unions  are  called: 


OF    THE 

UNIVERSITY 

17 


Marsh  Gas,  or  Carburetted  Hydrogen,  and 

Olefiant  Gas,  or  Bi-carburetted  Hydrogen. 

Marsh  Gas  consists  of  one  atom  of  carbon  and  four  of  hydrogen, 
and  the  atomic  weight  is  12+4=  16.  The  chemical  symbol  is  CH4. 

Olefiant  Gas  consists  of  two  atoms  of  carbon  and  four  of  hydro- 
gen, and  the  atomic  weight  is  12+12+4  =  28.  The  chemical 
symbol  is  C2H4. 

Atmospheric  air  is  a  mixture  composed  principally  of  oxygen 
and  nitrogen.  Neglecting  moisture,  impurities  and  decimals,  the 
components  are  found  mixed  in  the  following  average  proportions: 

Oxygen 23  parts  by  weight 

Nitrogen 77     "      " 

or 

Oxygen 21     "      "  volume 

Nitrogen 79     "      "        " 

As  the  gases  are  driven  off  from  the  coal,  due  to  the  absorption 
of  latent  heat,  they  become  mixed  with  the  entering  air.  The 
result  is  that  the  hydrogen  separates  from  the  carbon  and  unites 
with  the  oxygen,  forming  water,  or,  more  correctly  speaking,  vapor 
of  water.  The  now  free  carbon  also  unites  with  oxygen  in  the 
formation  of  carbon  dioxide  (CO2).  Both  of  these  combinations 
are  productive  of  heat,  thus  making  the  process  continuous. 

After  the  hydrocarbon  element  has  been  separated  in  the  form 
of  gas,  the  coal  remaining  on  the  grate  is  composed  chiefly  of  solid 
carbon.  This  is  consumed  by  uniting  with  the  oxygen  in  the  air 
which  passes  up  between  the  grate-bars.  The  union  of  the  carbon 
with  the  oxygen  may  be  in  two  proportions,  forming  bodies  having 
very  different  characteristics. 

If  two  atoms  of  oxygen  unite  with  one  atom  of  carbon,  the 
result  is  carbon  dioxide.  But  if  one  atom  of  oxygen  only  unites 
with  one  atom  of  carbon,  the  resulting  formation  is  carbonic  oxide 
or  carbon  monoxide.  This  monoxide  may  yet  unite  with  another 
atom  of  oxygen,  and  when  it  does  its  combustion  will  be  complete. 

If,  however,  this  carbon  monoxide  does  not  meet  with  the 
necessary  oxygen  while  within  the  furnace,  it  will  pass  away  only 
half  burned. 

The  same  result  is  attained  in  cases  where  a  particle  of  free 
carbon  meets  with  another  of  carbon  dioxide,  when  two  particles 


18 


STEAM-BOILERS 


of  carbon  monoxide  will  be  formed.  Should  there  still  be  lacking 
the  necessary  oxygen,  then  two  particles  of  half-burned  carbon 
will  pass  into  the  stack.  This  latter  case  is  continually  happening 
where  the  air  has  to  pass  upward  through  a  thick  mass  of  incan- 
descent carbonaceous  matter.  The  air  entering  through  the  hot 
grate-bars  becomes  heated,  and  its  oxygen  unites  with  the  incan- 
descent carbon,  forming  carbon  dioxide,  thereby  producing  heat 
which  keeps  the  layer  next  to  the  grate  in  an  incandescent  state. 
This  carbon  dioxide,  at  a  high  temperature,  then  has  to  pass 
upward  through  the  layer  of  solid  carbonaceous  matter  above,  and 
it  takes  up  an  additional  portion  of  carbon,  forming  two  particles 
of  carbon  monoxide  (CO2+C  =  2CO).  See  Fig.  2. 


Air  odirjifted  above  Grate 


Air 


FIG.  2. — Combustion  on  Grate. 


In  this  operation  heat  is  absorbed,  and  there  is  also  lost  an 
extra  portion  of  carbon,  unless  the  monoxide  meets  with  more 
oxygen  to  complete  its  combustion. 

This  illustrates  why  there  always  should  be  an  excess  of  air 
passing  through  the  furnace,  and  the  possible  advantage  of  having 
some  air  supplied  above  the  grate  or  back  of  the  bridge  wall.  Fur- 
thermore, the  thickness  of  fire  should  be  only  sufficient  to  cover  the 
grate  properly  and  prevent  too  much  air  from  passing.  Thin 
fires  have  the  disadvantage  of  burning  through  in  spots,  and  are 
not  liked  by  the  firemen,  who  are  thus  compelled  to  maintain  a 
close  watch.  Better  results  are  obtained  by  using  a  thin  fire,  and 
supplying  fresh  charges  at  short,  regular  intervals,  rather  than  by 
a  complete  spreading  with  heavier  charges  at  longer  intervals. 


COMBUSTION  19 

There  is  another  peculiarity  of  this  carbon  monoxide,  namely, 
that  it  will  inflame  at  a  lower  temperature  than  the  coal-gases 
(CH4  and  C2H4),  due  to  its  having  already  united  with  half  its  full 
capacity  for  oxygen.  Consequently  when  the  oxide  has  passed 
into  the  flues  or  has  come  into  contact  with  the  comparatively 
cool  boiler  surfaces,  its  temperature  is  often  reduced  below  that 
required  to  burn  the  coal-gases,  but  is  still  hot  enough  to  take  up 
an  extra  portion  of  oxygen,  which  it  frequently  does  on  reaching 
the  top  of  the  chimney,  where  it  becomes  ignited  on  meeting  the 
air.  This  explains  the  red  flame  so  often  seen  at  the  top  of  chim- 
neys, and  necessarily  the  heat  there  generated  is  entirely  lost  for 
the  purposes  of  the  boiler. 

The  temperatures  at  which  some  of  the  physical  and  chemical 
changes  take  place  when  a  fresh  charge  of  coal  is  thrown  on  a  fire 
are  about  as  follows :  * 

(a)  Previous  to  putting  on  a  charge  of  coal  the  temperature  of  the 
bed  of  coals  is  from  dull  red  heat  (700°  C.  or  1292°  F.)  up  to  a  bright 
white  heat  (1400°  C.  or  2552°  F.)  or  even  higher. 

(6)  The  coal,  when  fired,  is  about  15°  C.  or  60°  F.  (temperature  of 
the  room).  As  soon  as  it  reaches  the  fire-bed  it  begins  to  heat  by  con- 
duction from  the  hot  coals  beneath.  The  hot  gases,  products  of  com- 
bustion of  the  coal  beneath,  also  heat  the  new  charge  of  coal. 

(c)  The  heating  of  the  coal  causes  the  volatile  matter  to  distil  off. 
The  amount  distilled  at  any  given  temperature  is  unknown,  but  it  is 
certain  that  traces  of  volatile  combustible  matters  are  given  off  as  low 
as  110°C.  (220°  F.). 

(d)  At  about  400°  C.  or  750°  F.  the  coal  reaches  the  temperature  of 
ignition  and  burns  to  carbon  dioxide. 

(e)  At  about  600°  C.  or  1100°  F.  most  of  the  gases  given  off  by  coal 
(hydrogen,  marsh-gas    and  other  volatile  hydrocarbons)  will  ignite  if 
oxygen  be  present. 

(/)  At  800°  C.  (1470°  F.)  the  carbon  dioxide,  as  soon  as  formed  from 
the  coal,  will  give  up  one  atom  of  its  oxygen  to  burn  more  coal,  thus: 
CO2  +  C  =  2CO.  This  carbonic  oxide  will  burn  back  to  carbon  dioxide 
if  mixed  with  oxygen  at  the  necessary  temperature,  which  is  between 
650°  and  730°  C.  (1200°  and  1350°  F.). 

(g)  At  about  1000°  C.  or  1832°  F.  the  H2O  formed  by  the  burning 
of  the  hydrogen  in  the  volatile  matter  in  the  coal  begins  to  dissociate. 


*  Steam  Users'  Association,  Boston,  Circular  No.  9.     11.  S.  Rale's  Report 
on  Efficiency  of  Combustion. 


20  STEAM-BOILERS 

(h)  At  about  1000°  C.  or  1832°  F.  any  carbon  dioxide  not  previously 
burned  to  carbonic  oxide  begins  to  dissociate  to  carbonic  oxide  and 
oxygen. 

(i)  The  various  hydrocarbons  which  begin  to  be  distilled  at  110°  C., 
and  possibly  lower,  undergo  many  changes,  dissociations  and  breakings 
up  at  the  various  temperatures  they  pass  through.  So  many  of  these 
are  unknown  that  it  is  useless  to  state  the  few  we  do  know. 

Above  700°  C.  (1300°  F.)  both  the  hydrocarbons  and  the  carbonic 
oxide  will  unite  with  oxygen  if  the  latter  be  present  and  intimately  mixed 
with  them.  If  they  do  not  burn,  the  tendency  is  always  to  break  up 
into  simpler  and  more  volatile  compounds  as  the  temperature  rises. 

The  above  statements,  however,  give  only  the  properties  of  the  coal, 
and  the  chemical  reactions  it  is  capable  of  at  the  different  temperatures 
it  passes  through.  Its  actual  combustion  depends  on  the  supply  of 
oxygen  as  well  as  on  the  condition  of  the  coal  at  any  given  time.  The 
oxygen  is  practically  all  supplied  from  the  air,  the  amount  of  oxygen 
present  in  the  coal  being  so  small  as  to  be  of  no  present  importance,  even 
if  it  is  not  already  in  chemical  combination  with  the  carbon  or  hydrogen. 

The  temperatures  at  which  some  of  the  combinations  mentioned 
take  place  were  determined  by  Mallard  and  Le  Ch  atelier,  who  pub- 
lished two  articles  in  the  Annales  des  Mines,  Vol.  IV,  1883,  pp. 
274,  379-559.  In  these  experiments,  mixtures  of  H  and  O,  CO 
and  O,  and  marsh-gas  and  O  were  placed  in  a  closed  chamber  which 
was  heated  externally.  They  found  that  the  hydrogen  and  oxy- 
gen ignited  at  555°  C.,  the  CO  and  O  at  655°  C.,  and  the  marsh- 
gas  at  650°  C. 

The  results  were  found  to  be  independent  of  the  proportions 
of  the  gas  in  the  mixture.  It  was  also  found  that  the  presence 
of  an  inert  ga,s  such  as  N  did  not  alter  the  results,  with  the  excep- 
tion that  a  large  amount  of  C02  in  the  mixture  of  CO  and  0  elevated 
the  ignition  temperature  from  655°  C.  to  700°  C. 

With  the  H  and  CO  mixed  with  0  the  combustion  ensued  im- 
mediately on  exposure  to  the  temperature  of  ignition,  whereas 
with  the  CH4  there  was  a  lag  in  the  ignition,  time  being  required 
to  ignite  the  gas  after  it  was  brought  to  the  temperature  of  ignition. 
The  above  was  taken  from  a  brief  account  of  the  investigation 
given  in  the  Chemical  Technology,  Vol.  I,  Groves  and  Thorp. 

While  discussing  the  subject  of  combustion  it  will  be  well  to 
recall  the  laws  of  Avogadro  (1811),  which  may  be  expressed  thus: 
"The  molecules  of  all  gases,  simple  or  compound,  occupy  equal 


COMBUSTION 


21 


volumes ;  or  equal  volumes  of  all  gases  contain  under  similar  con- 
ditions of  temperature  and  pressure  the  same  number  of  mole- 
cules." "The  molecules  of  compound  bodies  in  the  gaseous  state, 
with  but  few  exceptions,  occupy  twice  the  volume  of  an  atom  of 
hydrogen."  From  this  reasoning,  the  volume  of  CO  is  equal  to 
twice  the  volume  of  CO2  producing  it.  That  is,  when  a  particle  of 
carbon  burns  into  CO2  and  then  meets  another  particle  of  carbon, 
the  volume  of  the  monoxide  formed  will  be  twice  the  volume  of 
the  original  dioxide.  This  fact  accounts  for  the  loss  in  available 
heat.* 

Furthermore,  the  production  of  carbon  monoxide  will  require 
the  same  volume  as  if  the  carbon  were  burned  to  the  dioxide,  and 
while  equally  rilling  the  flues  and  choking  the  draft,  will  only  gen- 
erate about  one-third  the  heat. 

The  requirements  for  perfect  combustion  are  a  surplus  of  air, 
a  thorough  mixture  of  the  fuel-particles  with  the  oxygen  in  the 
air,  and  a  high  temperature.  A  furnace  that  fails  to  offer  any  or 
all  of  these  conditions  will  not  support  perfect  combustion. 

The  products  of  combustion  are,  therefore,  carbon  dioxide, 
carbon  monoxide,  vapor  of  water,  the  oxides  of  impurities  in  the 
fuel,  oxygen,  nitrogen  and  ash. 

The  composition  of  the  gases  from  combustion  may  be  found 
in  almost  any  ratio.  The  following  volumetric  analyses  will  afford 
some  idea  of  the  ratio  found.  The  last  two  are  given  on  the  author- 
ity of  George  H.  Barrus,  the  last  one  being  the  products  from  Poca- 
hontas  (semi-bituminous)  coal: 


Poor. 

Average. 

Excellent. 

Carbon  dioxide  (CO2)  

8.0% 
4.4 
7.6 

80.0 

9.0% 
11.5 
Trace 

79.5 

12.0% 
7.5 
0.1 

80.4 

15.1% 
4.0 
0.7 

80.2 
100.0 

Oxvgen  (O)  

Carbon  monoxide  (CO)  

Nitrogen,  vapor  of  water,  etc.,  by 
difference  

100.0 

100.0 

100.0 

These  gas  analyses  can  be  made  by  the  Orsat  or  some  similar 
apparatus,  by  tapping  the  flue  and  extracting  a  measured  volume 


*  See  Rankine,  Steam-engines,  p.  270. 


22  STEAM-BOILERS 

by  means  of  a  pressure-bottle,  such  as  is  used  in  a  chemical  labo- 
ratory, and  a  graduated  burette.  The  sample  is  then  forced  in 
succession  through  three  pipettes  containing  caustic  potash,  pyro- 
gallic  acid  and  caustic  potash,  and  cuprous  chloride  in  hydro- 
chloric acid,  which  will  absorb  respectively  the  carbon  dioxide,  the 
oxygen  and  the  carbon  monoxide.  The  loss  of  volume  at  each 
operation  is  measured  in  the  burette. 

From  a  gas  analysis,  the  air-supply  to  the  furnace  can  be 
closely  calculated,  as  will  be  shown  later. 

The  Refuse  from  a  fuel  is  that  portion  which  falls  into  the  ash- 
pit and  that  carried  off  by  the  draft,  consisting  of  ashes,  unburnt 
or  partially  burnt  fuel  and  cinders. 

The  following  is  from  a  report  of  R.  S.  Hale,  Steam  Users'  Asso- 
ciation, Boston,  Circular  No.  9: 

"  The  amount  of  loss  by  unburned  coal  in  the  ash-pit  depends  on  so 
many  factors  that  it  is  impracticable  to  express  it  by  any  formula.  A 
statement  of  the  factors  and  a  collection  of  examples  must,  therefore, 
suffice. 

"(a)  The  loss  by  unburned  c6al  in  the  ash-pit  depends  on  the  width 
of  the  opening  in  the  grate-bars,  and  increases  as  the  width  increases. 

"(6)  The  loss  depends  on  the  size  of  the  coal,  and  increases  as  the 
size  of  the  coal  decreases. 

"(c)  The  loss  is  probably  greater  for  a  non-caking  than  for  a  caking 
coal. 

"(d)  The  loss  probably  increases  as  the  amount  of  earthy  matter  in 
the  coal  increases,  but  not  at  the  same  ratio. 

"(e)*  The  loss  is  less  with  a  fan-blast  than  with  a  steam-blast. 

"(/)*  The  loss  is  greater  the  more  the  fire  is  disturbed.  This  is  espe- 
cially noticeable  in  automatic  stokers  with  moving  grate-bars. 

"When  determining  the  amount  of  carbon  or  combustible  in  the  refuse, 
taking  the  difference  between  the  amount  of  refuse  shown  by  the  boiler 
test  and  the  amount  of  earthy  matter  shown  by  analysis  of  a  sample  of 
the  coal  is  not  sufficient,  for  two  reasons :  first,  the  sampling  of  the  coal 
may  easily  be  in  error;  and  second,  a  considerable  amount  of  earthy 
matter  is  at  times  carried  into  the  flues  and  even  up  the  chimney." 

*"  Report  of  Coal  Waste  Commission,  Pa.,  1893,  p.  31. 


COMBUSTION 
TABLE  V 

LOSS    BY    UNBURNED    COAL    IN    ASH-PIT 


23 


Remarks  —  Authority. 

Per  Cent 
Refuse. 

Per  Cent 
Combus- 
tible in 
Refuse. 

Per  Cent  in 
Total  Coal. 

E.  B.  Coxe  (Trans.  N.  E.  Cotton  Mfg.  Assn., 
1  895)  ,  using  his  travelling  grate,  on  small- 
sized  anthracite  coal.        

(  10.05 
|  23.70 

18.68 
11.92 

2.2 
2.7 

W.  H.  Bryan  (Trans.  A.  S.  M.  E.,  Vol.  XVI, 
p  773)  us>inop  soft  coal 

j  13.35 
\  14  31 

31.0 
25  0 

4.3 
3  6 

Pennsylvania  coal,  bars  1|  in.  wide,  1  in.  apart. 
Other  'tests  ."•*.. 

16.10 
10.30 

25.0 
37.2 

4.0 
3.8 

u         it 

9.20 

31.3 

2.9 

u        (i 

18.50 

29.3 

5.4 

f(         "     with  a  mechanical  stoker  .        ... 

13  61 

67  8 

9  2 

ie           ((          <t      u              (e                    u 

Arkansas  State   Geological  Survey  Report, 
1888,  Vol.  Ill,  p.  73.     Pittsburg  coal..  .  . 
Ditto      Arkansas  roal                   

18.70 

8.10 
10  30 

67.2 

26.0 
30  0 

12.6 

2.1 
3  1 

«                 (t           a 

40  00 

83  0 

33  2 

(i                 tt           a 

14.00 

51  4 

7  2 

Dampfkessel  Revision  Verein  Berlin  Geschafts 
Bericht  1895,  p  79.     Coal-dust  

4.8 

50.0 

2  4 

The  quantity  of  air  required  for  the  complete  combustion  of 
the  principal  elements  of  a  fuel  may  be  determined  as  follows : 

CARBURETTED  HYDROGEN — MARSH-GAS — CH4. 


Before  Combustion. 

Weight.                    Atoms. 

Weight. 

1     Carbon 

12 

1     Hydrogen 

1      ' 

CH4    16 

1     Hydrogen 

1 

1     Hydrogen 

1      ' 

1     Hydrogen 

1 

1     Oxygen 

16     ' 

1     Oxygen 

16      ' 

Air  278+  - 

1     Oxygen 

16      ' 

1     Oxygen 

16 

L  15.3  Nitrogen 

214+ 

After  Combustion. 
Weight. 


294+ 


294+ 


Carbonic  Acid 
Water 


Water 


214+   Free  Nitrogen 
294+ 


From  this  diagram  it  will  be  noted  that  for  every  16  parts  by 
weight  of  marsh-gas  278+ parts  of  air  are  required  for  complete 
combustion;  or  for  every  one  pound  of  marsh-gas  17.4  pounds  of 
air  are  required. 


24 


STEAM-BOILERS 


Bl-CARBURETTED    HYDROGEN OLEFIANT    GAS C2H4 


Before  Combustion. 

Weight.                     Atoms. 

'      1  Carbon 

1  Carbon 

C2H4  28 

1  Hydrogen 

1  Hydrogen 

1  Hydrogen 

1  Hydrogen 

1  Oxygen 

1  Oxygen 

1  Oxygen 

Air  417+  < 

1  Oxygen 

1  Oxygen 

1  Oxygen 

„   23  Nitrogen 

445+ 


445+ 


After  Combustion. 
Weight. 

44  Carbonic  Acid 

44  Carbonic  Acid 

18  Water 

18  Water 


321+   Free  Nitrogen 

445+ 


From  this  diagram  it  will  be  noted  that  for  every  28  parts  by 
weight  of  olefiant  gas,  417+  parts  of  air  are  required  for  complete 
combustion;  or  for  one  pound  of  olefiant  gas  14.9  pounds  of  air 
are  required. 

Air  Required  to  Burn  One  Pound  of  Carbon.  If  the  combus- 
tion be  perfect,  the  air  required  to  burn  one  pound  of  carbon  will 
have  to  be  sufficient  to  change  the  carbon  into  carbon  dioxide. 
The  composition  of  the  dioxide  is,  by  weight,  12  parts  carbon  and 
32  parts  oxygen,  or  one  part  carbon  and  2.67  parts  oxygen. 

Also  there  are,  by  weight,  0.23  parts  of  oxygen  in  one  part  of  air. 

Therefore  one  pound  of  carbon  will  require 


0.23  :  1  :  :  2.67  :  x  =        =  11.61  Ibs.  of  air. 

O.Zo 

If  the  carbon  be  imperfectly  burned,  it  will  be  changed  to  the 
monoxide;  and  the  composition  of  the  oxide  is,  by  weight,  12 
parts  carbon  and  16  parts  oxygen,  or  one  part  carbon  and  1.33 
parts  oxygen. 

Therefore,  for  imperfect  combustion,  one  pound  of  carbon  will 
require 

1.33 
:O23 


0.23  :  1  ::  1.33  :  x 


^  5.78  Ibs.  of  air. 


Air  Required  to  Burn  One  Pound  of  Hydrogen.  When  hydro- 
gen is  burned  it  forms  a  union  with  oxygen,  the  product  of  which 
is  water.  The  relative  weights  of  the  combining  volumes  are  in 


COMBUSTICW  25 

the  ratio  of  two  parts  hydrogen  to  sixteen  parts  oxygen,  or  one 
part  hydrogen  to  eight  parts  oxygen,  making  nine  parts  water. 
Therefore  one  pound  of  hydrogen  will  require 

0.23  :  1  :  :  8  :  x  =  ^  =  34.78  Ibs.  of  air. 
(j.2o 

The  Volume  of  Air  Required  for  Combustion.  Since  it  requires 
11.61  pounds  of  air  to  burn  one  pound  of  carbon,  and  since  the  vol- 
ume of  one  pound  of  dry  air  at  62°  F.,  with  a  barometric  pressure 
of  29.92  inches  of  mercury,  is  13.141  cubic  feet,  the  volume  of  air 
required  for  combustion  at  stated  temperature  and  pressure  is 

1  1.  61  X  13.141  =  152.56  cubic  feet  per  pound. 

By  a  similar  course  of  reasoning,  the  volume  required  for  the 
combustion  of  hydrogen  is 

34.78X  13.141-457.04  cubic  feet  per  pound. 

The  following  formula  of  Dulong  is  convenient  for  determining 
the  theoretical  quantity  of  air  that  is  required  for  the  combustion 
of  any  fuel  whose  composition  is  known. 

Let  C,  H  and  O  denote  respectively  the  weight  of  carbon,  hy- 
drogen and  oxygen  in  the  fuel;  and  W  and  V  the  weight  and  vol- 
ume of  air  required.  Other  ingredients  may  be  neglected,  as  they 
have  but  a  slight  effect  on  the  result.  Then 


-        or 


TF=12C+35/H-9     nearly;  and 

\ 


7=152.560+  457.04  H-        or 

\         o/ 

7=153C+457fH-^V  nearly. 
\       <V 

The  value  of  W  per  pound  is  about  12  for  anthracite  and  good 
bituminous  coals,  6  for  wood,  and  11  for  charcoal. 

It  is  found  impossible  in  practice  to  obtain  complete  combus- 
tion unless  the  air  supplied  to  the  furnace  be  in  excess  of  that 


26  STEAM-BOILERS 

theoretically  required.  Experience  dictates  that  for  ordinary 
natural  draft  nearly  twice  the  theoretical  quantity  of  air  should 
be  admitted,  or  about  24  pounds  per  pound  of  coal.  With 
mechanical  drafts  and  with  natural  drafts  when  the  mixing 
effects  are  strong  and  positive,  the  excess  of  air  may  be  consider- 
ably reduced. 

The  volume  of  air-supply  per  pound  of  coal,  in  ordinary  factory 
practice,  with  natural  draft  is  about  300  cubic  feet;  and  may  be 
as  low  as  200  cubic  feet  when  the  mixing  effect  is  strong. 

The  actual  volume  may  be  estimated  by  using  an  anemometer, 
or  may  be  closely  calculated  from  a  gas  analysis.  This  calculation 
is  best  illustrated  by  an  example. 

Take  the  gas  analysis,  marked  average,  in  a  previous  para- 
graph, and  consider  the  percentages  of  volume  as  cubic  feet  in  one 
hundred  of  gas.  The  weights  can  be  determined  from  the  den- 
sities given  in  Table  I. 

Vols.     Density.    Weights. 

For  C02 12.0X0.1227  =  1.47240 

"    0 7.5X0.0892  =  0.66900 

"    CO. 0.1X0.0782  =  0.00782 

These  weights  can  be  subdivided  into  those  of  their  constituents; 
thus  the  CO2  contains  by  weight  T3T  of  carbon  and  -fa  of  oxygen, 
and  the  CO,  f  of  carbon  and  $  of  oxygen. 

T8TX  1.47240  =  1.07084  T3TX  1.47240  =  0.40156 

£X  0.00782  =  0.00446  f  X  0.00782  =  0.00335 

0.66900 


Pounds  of  oxygen,  .  .  .    1.74430        Pounds  of  carbon,  .  .  .    0.40491 

1  74430 
Therefore  the  oxygen  per  pound  of  carbon  is    '  =  4.30  Ibs. 

\)  •  ±\)±\s  JL 

Again,  since  air  contains  0.23  parts  of  oxygen,  the  air  per  pound 

4  30 
of  carbon  is  ^^7^-  =  18. 7  Ibs. 

O.Zo 

As  above  reasoning  assumes  that  all  the  surplus  air  is  charged 
to  the  carbon,  the  final  result  will  have  to  be  increased  by  the 
theoretical  amount  necessary  to  burn  the  hydrogen. 

Assume  that  the  analysis  of  the  coal  was:  carbon  87%,  hydro- 


COMBUSTION  27 

gen  2%,  oxygen  3%  and  ash  8%.      Then  the  air  in  pounds  sup- 
plied will  be: 

For  carbon 0.87X18.7  =  16.27 

"    hydrogen 35(o.02-?|^  =   0.57 

Air  per  pound  of  coal =  16.84  Ibs. 

The  theoretical  amount  of  air  for  combustion  would  have  been 

TF=  12X0.87+ 35 (^0.02- 5^?  1-11.01  Ibs.,  and  therefore  the  sur- 

\  8    / 

plus  was  5.83  Ibs.,  or  about  53  per  cent. 

The  Methods  for  Charging  coal  are  known  as  the  alternate, 
spreading  and  coking  firings,  in  accordance  with  the  way  in  which 
the  fuel  is  spread  upon  the  grate. 

(a)  The  Alternate  Method  consists  of  charging  the  fresh  coal 
on  one  side  of  the  fire  at  a  time,  so  that  the  gases  evolved  can  be 
burned  by  the  excess  of  air  passing  through  the  other  side,  which 
is  at  a  bright  heat.  With  boilers  having  two  or  more  furnaces 
and  a  common  combustion-chamber  this  is  practically  accom- 
plished by  firing  only  one  furnace  at  a  time.  This  method  oper- 
ates most  effectively  when  the  flow  of  the  gases  is  such  as  to  pro- 
duce a  thorough  mixture. 

(6)  The  Spreading  Method  consists  of  charging  a  thin  layer  of 
coal  over  the  whole  grate  at  each  firing.  When  the  gases  have  to 
rise  vertically  this  method  is  generally  considered  better  than  the 
alternate  method.  It  may  be  modified  by  sprinkling  the  charge 
in  patches  instead  of  covering  the  whole  surface.  This  latter 
method  is  better  than  a  complete  spreading,  and  with  the  ordinary 
firemen  will  give  more  economical  results. 

(c)  The  Coking  Method  consists  of  charging  the  fresh  coal  on 
the  dead  plate  at  the  front  of  the  fire,  and  pushing  back  the  coked 
fuel  to  make  room  for  the  new  charge.  This  method  is  only  advan- 
tageous when  the  gases  evolved  pass  over  the  bright  part  of  the 
fire.  It  is  of  little  or  no  use  when  the  gases  have  to  rise  vertically. 
It  is  also  a  difficult  method  and  requires  a  fairly  good  fireman  to 
make  it  effective. 

Much  depends  on  the  fuel  and  the  furnace  design,  but  in  gen- 
eral the  spreading  method  is  the  best  and  then  the  alternate.  In 


28  STEAM-BOILERS 

any  case  the  charges  should  be  in  small  quantities  at  frequent  inter- 
vals. 

The  Thickness  of  Fire  varies  from  about  three  inches  to  about 
sixteen  inches.  Fine  sizes  of  coal  must  be  used  in  thin  fires,  as 
they  pack  so  close  as  greatly  to  restrict  the  draft.  A  thick  fire 
requires  more  air  admitted  above  the  grate  to  consume  the  carbon 
monoxide  than  does  a  thin  fire.  It  is  best  to  use  as  thin  a  fire  as 
the  coal  will  permit.  Thick  fires  being  more  easy  to  handle  are 
preferred  by  firemen.  Thin  fires  require  closer  attention  to  pre- 
vent holes  being  burned  in  spots,  and  less  readily  respond  to  sudden 
calls  for  steam. 

A  thin  fire  has  the  simplicity  of  letting  all  the  air  required 
pass  through  the  grate,  which  is  thus  warmed  and  mixed  to  best 
advantage.  When  the  gases  rise  vertically  it  is  very  difficult, 
unless  complicated  methods  be  adopted,  properly  to  admit  air 
above  the  grate  and  accomplish  a  complete  mixture. 

A  Jet  of  Steam  admitted  above  or  below  the  fire  has  no  corre- 
sponding advantage  unless  it  be  strong  enough  to  produce  an 
artificial  draft.  A  small  jet  is  an  uneconomical  method  in  the  use 
of  steam.  The  steam  may  produce  water-gas,  but  no  additional 
heat  is  produced  thereby.  It  may  prevent  clinkering  with  some 
of  the  cheap  fuels,  and  may  reduce  the  smoke  by  a  process  of 
collection  of  the  particles,  but  no  economy  is  effected  over  the 
cost  of  the  steam  used.  For  similar  reasons  water  is  sometimes 
put  in  the  ash-pit  or  the  fuel  purposely  wet.  Both  these  latter 
methods  are  sources  of  direct  loss. 

The  conclusions  drawn  by  R.  S.  Hale*  are:  That  ordinary 
firing  is  apt  to  give  10  to  20  per  cent  worse  results  than  the  best 
skilled  firing,  the  low  results  being  caused  by  using  too  much  air 
and  by  getting  poor  combustion. 

That  it  is  easier  for  firemen  to  get  better  results  in  some  boiler- 
furnaces  than  others,  but  that  this  difference  becomes  large  only 
with  poor  soft  coal. 

That  many  but  not  all  of  the  patent  devices  (down-draft 
grates,  stokers,  etc.)  in  common  use  will  with  moderately  skilled 
firemen  give  better  results  than  those  obtained  by  ordinary  firemen 
in  ordinary  furnaces. 

*  Steam  Users'  Circular  No.  9. 


COMBUSTION  29 

That  it  is  probable,  but  not  proved,  that  ordinary  firemen  can 
get  better  results  from  these  devices  than  can  ordinary  firemen  on 
ordinary  grates. 

Heat  of  Combustion.  The  heat  produced  by  the  combustion 
of  one  pound  of  various  substances  is  given  in  the  following  table 
in  British  heat-units: 

TABLE  VI 

TOTAL    HEATS    OF    COMBUSTION 

Hydrogen  gas 62,032 

Carbon  to  carbon  dioxide 14,500 

Carbon  to  carbon  monoxide 4,400 

Carbon  monoxide  to  carbon  dioxide 4,330 

Olefiant  gas 21,344 

Liquid  hydrocarbons  vary  in  proportion  to  weight  from  19.000 

to  22,600 

Charcoal,  wood 13,500 

peat 11,600 

Wood,  dry average  7,800 

"       20%  moisture 6,500 

Peat,  dry average  9,950 

"      25%  moisture 7,000 

Coal,  anthracite,  best  qualities about  15,000 

ordinary "  13,000 

"      bituminous,  dry.  . "  14,000 

"      cannel "  15,000 

"      ordinary  poor  grades "  10,000 

These  figures  are  slightly  altered  by  different  authors.  The 
above  list  may  fairly  be  taken  as  an  average. 

The  heating-power  of  any  fuel,  that  is,  its  total  heat  of  com- 
bustion, is  determined  by  calculation  or  by  actual  measurement 
in  a  calorimeter.  This  quantity  is  the  sum  of  the  amounts  of  heat 
generated  by  the  combustion  of  the  unoxidized  carbon  and  hydrogen 
contained  in  the  fuel,  less  the  heat  required  in  the  evaporation  and 
volatilization  of  those  constituents  which  become  gaseous  at  the 
temperatures  resulting  from  the  combustion  of  the  first-named  con- 
stituents. 

The  heating-power  may  be  expressed  for  nearly  all  practical 
purposes  with  sufficient  accuracy  by  the  formula  of  MM.  Favre 
and  Silbermann,  as  follows: 

Total  heat  of  combustion  in  B.  T.  U.  =  14,5000+  62,032  ^H- 

in  which  C,  H  and  O  represent  the  proportions  by  weight  of  car- 
bon, hydrogen  and  oxygen  contained  in  the  fuel.     One-eighth  of 


30  STEAM  BOILERS 

the  weight  of  oxygen  is  subtracted  from  the  hydrogen,  because 
oxygen  and  hydrogen  unite  in  that  proportion  to  form  water,  and 
when  present  in  that  proportion  are  useless  for  the  production 
of  heat. 

Later  experiments  show  that  a  closer  agreement  to  calorimetric 
results  is  obtained  by  modifying  the  coefficients,  thus: 

Total  heat  -14,6000  +  62,000  (H-  Q\  +4000S, 


in  which  C,  H,  0  and  S  represent  the  proportions  of  carbon,  hydro- 
gen, oxygen  and  sulphur. 

An  approximate  formula,  which  will  be  found  convenient  for 
agents  purchasing  coals,  because  the  percentages  of  ash  and  moisture 
are  easily  obtainable,  is  in  use  in  the  following  form: 

Total  heat  of  combustion  =  h  = 

154.8  ]  100  —  (per  cent  of  ash  +  per  cent  of  moisture)}. 


CHAPTER  III 
FUELS 

Coal.  Classification.  Anthracite.  Semi-anthracite.  Semi-bituminous. 
Bituminous.  Dry  Bituminous.  Bituminous  Caking.  Long-flaming  Bitu- 
minous. Lignite.  Size  of  Coal.  Culm.  Weight  of  Coal.  Feat  or  Turf. 
Wood.  Coke  and  Charcoal.  Miscellaneous  Fuels.  Sawdust.  Straw. 
Bagasse.  Protection  from  Weather.  Chemical  Composition  of  Coals. 
Liquid  Fuels.  Gaseous  Fuels. 

EVERY  form  of  fuel  is  especially  suitable  for  particular  purposes 
and  conditions,  whether  it  be  in  a  solid,  a  liquid  or  a  gaseous  state. 

In  making  his  selection,  the  engineer  must  choose  the  one  best 
adapted  to  the  work  in  hand,  taking  into  consideration  all  the  cir- 
cumstances that  may  affect  its  use.  The  selection  is  often  depen- 
dent on  the  ease  or  difficulty  with  which  it  can  be  procured,  as 
well  as  its  cost.  The  cost  frequently  prevents  the  best  fuel  from 
being  used;  for,  although  less  may  be  required,  still  the  price  may 
be  so  high  as  to  render  a  larger  quantity  of  some  cheaper  grade 
more  economical. 

Having  made  a  selection  of  kind  and  quality,  the  engineer 
then  designs  the  boilers  and  furnaces  to  suit. 

Coal.  All  coals  are  of  vegetable  origin,  being  the  long-decayed 
product  of  ancient  forests.  Although  coal  has  undergone  a  com- 
plete change  from  its  original  state,  its  chemical  composition  often 
is  little  altered.  However,  coal  is  sometimes  found  so  mixed  with 
earthy  matters  that  its  value  as  a  fuel  is  entirely  lost. 

When  burned,  the  organic  matter  is  resolved  into  its  various 
component  parts,  consisting  of  carbon,  hydrogen  and  oxygen, 
combined  in  formation  of  various  substances,  as  carbon,  tar,  am- 
monia, benzole,  naphtha,  paraffine,  the  coal-gases  and  coke;  while 
the  inorganic  matter  remains  as  ash,  consisting  chiefly  of  the  sili- 
cates. 

31 


32 


STEAM-BOILERS 


It  is  difficult,  if  not  impossible,  to  distinguish  the  coals  by 
name  and  to  classify  all  varieties  under  proper  headings  or  sub- 
divisions, since  they  are  found  in  all  forms  intermediate  between 
that  of  recent  vegetable  growth  to  that  of  the  perfectly  mineralized 
state. 

The  classification  of  M.  L.  Gruner  is  as  follows :  * 


Name  of  Fuel. 

Ratio  |. 

Proportion  of 
Coke  or  Char- 
coal Yielded 
by  the  Dry 
Pure  Fuel. 

Anthracite  coals  

1  to  0  75 

90  to    92 

Bituminous  coals  

4  to  1 

50  to    90 

Lignite  or  brown  coals  

5 

40  to    50 

Peat  and  fossil  fuel  

6  to  5 

35  to    40 

Wood  (cellulose  and  en  casing  matter) 

7 

30  to    35 

Pure  cellulose 

8 

28  to    30 

A  general  classification  as  proposed  by  William  Kent,  based 
on  a  method  by  Prof.  Persifer  Frazer,  is  as  follows: 

The  "fuel  ratio"  or  " carbon  ratio"  is  the  ratio  the  fixed  car- 
bon bears  to  the  volatile  hydrocarbons.  This  arrangement  con- 
siders only  the  fuel  constituents  and  disregards  the  accidental 
impurities,  such  as  sulphur,  earthy  matter  and  moisture. 


Kind  of  Fuel. 

Fixed  Carbon, 
Per  Cent 

Volatile 
Hydrocarbons, 

Fuel  Ratio 
C. 

Per  Cent. 

V.H.C/ 

1.  Hard  dry  anthracite.  .  .  . 
2.  Semi-anthracite  

100        to  92.  31 
92  31  to  87  50 

0        to    7.69 
7  69  to  12  50 

100  to  12 
12  to    7 

3.  Semi-bituminous  

87  50  to  75  00 

12  50  to  25  00 

7  to    3 

4    Bituminous 

75  00  to    0 

25  00  to  100 

3  to    0 

Rankine  classifies  the  coals  thus:  Anthracite,  Semi-bituminous, 
Bituminous,  Long  Flaming  or  Cannel,  and  Lignite  or  Brown  Coal. 

Anthracite.  This  is  coal  in  its  most  perfect  form,  and  is  found 
in  the  oldest  carboniferous  strata.  Its  qualities  are  hardness  and 
compactness.  It  is  intermediate  in  color  between  jet-black  and 
plumbago.  It  is  amorphous  and  vitreous,  and  has  a  specific  grav- 
ity of  from  1.4  to  1.6.  While  having  a  high  calorific  value,  it  is 
difficult  to  "fire"  and,  when  fired,  to  keep  lighted.  Many  sam- 


*  Engineering  and  Mining  Journal,  25  July,  1874. 


FUELS  33 

pies  split  into  small  pieces  when  heated,  which  cause  a  consider- 
able loss  by  their  falling  into  the  ash-pit  through  the  grate-bars 
before  being  burned.  Being  free  from  the  hydrocarbons,  it  burns 
with  little  flame  and  produces  but  a  small  amount  of  smoke. 

The  percentage  of  refuse  varies  considerably,  and  the  loss  due 
to  "splitting"  often  increases  the  actual  amount  to  nearly  double. 
According  to  size  as  well  as  quality,  the  refuse  varies  from  five  to 
over  sixteen  per  cent,  the  coarser  sizes  giving  the  least  amount. 

Semi- anthracite.  This  is  a  coal  situated  between  the  pure 
anthracite  and  the  semi-bituminous.  It  is  less  amorphous  and 
more  lamellar  than  anthracite,  is  less  hard  and  burns  more  freely. 
It  can  generally  be  distinguished  by  its  tendency  to  soil  the  hands, 
while  pure  anthracite  will  not. 

Semi-bituminous.  This  is  the  next  grade  toward  bituminous 
coal.  It  burns  still  freer,  contains  more  volatile  hydrocarbon,  and 
is  a  valuable  steaming  coal. 

Bituminous.  This  grade  is  very  extensive,  and  contains  some 
very  valuable  varieties.  All  the  bituminous  coals  need  firing  with 
care  to  prevent  smoke  and  clinkers.  Some  of  the  grades  have  a 
very  high  calorific  value  and  are  much  used  for  steam  purposes. 

The  class  is  usually  divided  into  three  grades: 

(a)  Dry  Bituminous.  This  coal  has  a  specific  gravity  between 
1.25  and  1.40;  a  color  nearly  black,  with  a  resinous  lustre.  It  burns 
freely  and  kindles  with  much  less  difficulty  than  the  anthracites. 
It  is  hard,  but  weak  and  splintery.  It  gives  a  moderate  amount  of 
flame  and  but  little  smoke. 

(6)  Bituminous  Caking.  This  coal  has  a  specific  gravity  of 
about  1.25  and  contains  less  carbon  and  more  of  the  hydrocarbons 
than  the  former  class.  Its  color  is  less  black  and  more  resinous, 
and  there  is  less  tendency  to  splinter.  As  the  hydrocarbons  are 
driven  off,  this  coal  breaks  into  smaller  pieces  which  become  pasty 
and  finally  unite  into  large  solid  masses.  Unless  frequently  broken 
up  these  masses  check  the  draft.  The  flame  is  of  a  yellowish  color. 
It  is  a  valuable  coal  for  the  manufacture  of  gas  and  for  burning  in 
open  grates. 

(c)  Long-flaming  Bituminous.  This  coal  is  similar  in  many 
respects  to  the  latter  class,  but  contains  less  carbon  and  more 
hydrogen.  It  is  free-burning  with  a  long  yellowish  flame,  and  has 
a  strong  tendency  to  cake  or  form  clinkers. 


34 


STEAM-BOILERS 


Lignite.  This  variety  is  sometimes  called  " brown  coal"  on 
account  of  its  color.  It  is  really  coal  from  the  more  recent  geo- 
logical formations,  and  is  therefore  less  perfect.  Its  specific  gravity 
varias  from  1.10  to  1.25,  the  heavier  samples  containing  the  great- 
est percentage  of  earthy  matters.  It  kindles  with  ease  and  burns 
freely,  and  is  therefore  consumed  rapidly.  Its  structure  is  woody; 
it  is  lustreless,  contains  a  large  amount  of  water,  and  even  when 
dried  will  again  readily  absorb  large  quantities. 

It  forms  a  poor  fuel  when  judged  by  its  evaporating  power, 
but  is  largely  used  in  certain  localities  owing  to  its  cheap  cost. 

Size  of  Coal.  The  trade  distinguishes  the  sizes  by  certain 
names,  which  refer  to  the  dimensions  of  the  lumps  or  pieces  and  not 
to  the  grade. 

As  the  bituminous  coals  are  not  sold  according  to  size  they 
are  known  only  as  "run  of  mine"  or  "screened."  The  anthracites 
and  semi-anthracites  are,  however,  sold  under  trade  names,  which 
vary  somewhat  as  regards  the  dimensions  in  different  localities. 
The  "mesh"  of  the  screens  over  or  through  which  the  coal  passes 
while  being  separated  into  sizes  will  not  be  found  to  differ  ma- 
terially from  the  accompanying  list.  For  sizes  above  "broken 
coal "  bars  are  generally  employed  instead  of  screens.  Each  coal 
company  does  not  always  sell  all  the  listed  sizes,  but  more  often 
confines  itself  to  some  special  ones.  The  greatest  demand,  as 
measured  by  tonnage,  is  for  broken,  pea  and  buckwheat. 

LIST  OF-  SIZES  OF  ANTHRACITE  COAL 


Trade  Name. 

Size  of  Screen. 

Over. 

Through. 

Run  of  mine  .  .  . 

A 

Selecte 
4£  inc 
21 
21 

!j 

1 

A 

iV 

11  size 
5  in 
d  for 

lies 

DL 

5  mixed 
ches 
blast-fun 
7    inc 
4* 
2t      ' 
2* 
if 
IT 
I 

TS 

1* 

ist 

iace 
ties 

t 

Lump                      .    

Furnace  lump.                  

Steamboat  lump  

Broken  or  grate  .    .        

Egg  . 

Large  stove  or  stove  No.  1  

Small  stove    Qtovp  No  2  or  range 

Chestnut  

Pea  or  nut                                           .    . 

Buckwheat  or  buckwheat  No  1.  .  .                . 

Rice  or  buckwheat  No  2  .              

Barley  or  birdseye  .                 ..... 

Culm                                        .        ...        .          . 

FUELS 


35 


Culm.  This  is  the  name  given  to  the  refuse  dust  at  the  coal- 
mines. It  is  sometimes  called  " slack"  or  " breeze."  It  can  be 
bought  at  the  mines  at  very  low  rates,  as  it  is  difficult  to  transport, 
being  subject  to  heavy  loss  due  to  its  fineness.  Its  use  is,  there- 
fore, local.  Efforts  have  been  made  to  compress  this  dust  into 
briquettes,  but  so  far  its  adoption  has  been  but  limited.  Possi- 
bly a  successful  method  may  yet  be  invented. 

On  account  of  its  fineness,  culm  cannot  be  burned  on  the  ordi- 
nary grate.  There  are  various  methods  of  burning  it,  all  being 
based  on  the  principle  of  blowing  the  dust  into  the  furnace  with 
the  requisite  quantity  of  air.  It  then  burns  much  like  gas.  Some- 
times a  small  grate  is  used  on  which  there  is  the  usual  fire,  for  the 
purpose  of  igniting  the  dust-blast  in  case  the  flame  be  extinguished. 
For  best  results  the  culm  should  be  first  pulverized  to  a  fine  powder 
before  being  blown  into  the  furnace. 

TABLE  VII 

WEIGHT    PER    CUBIC    FOOT    OF    VARIOUS    COALS  * 


Weight  per 
Cubic  Foot, 
Pounds. 

Cubic  Feet 
per  Ton, 
2000  Pounds. 

Lehigh  lump 

55   26 

36  19 

cupola 

55  52 

36  02 

broken 

56  85 

35  18 

escsr 

57  74 

34  63 

stove 

58  15 

34  39 

nut                  .                             ..... 

58  26 

34  32 

pea                  ...             

53  18 

37  60 

buckwheat  

54  04 

37  01 

dust  

57  25 

34  93 

Free-burning  egg  

56  07 

35  67 

(f            stove 

56  33 

35  50 

"            nut  

56  88 

35  16 

Pittsburg 

46  48 

43  03 

Illinois 

47  22 

42  35 

Cornellsville  coke  

26  30 

76  04 

Hocking 

49  30 

40  56 

Indiana  block 

43  85 

45  61 

Erie   

48  07 

41  61 

49  18 

40  66 

When  Buying  Coals  it  is  well  to  remember  the  following  sug- 
gestions : 

(a)  The  heating  power  per  pound  of  combustible  of  the  com- 


*  Extract  from  bulletin  of  Anthracite  Coal  Operators'  Association  for 
November,  1897. 


36  STEAM-BOILERS 

bustible  portion  is  about  constant;  and  more  attention  should  be 
given  to  the  percentage  of  earthy  matter  contained  than  to  the 
calorific  power  per  pound  of  coal. 

(6)  The  percentage  of  earthy  matter  appears  to  increase  by 
about  1^  per  cent  for  each  size  of  coal,  as  it  becomes  smaller,  but 
the  price  often  diminishes  in  a  greater  ratio. 

(c)  The  amount  of  refuse  is  always  much  in  excess  of  the  earthy 
matter  as  reported  by  analysis. 

(d)  With  anthracites  the  best  qualities  are  indicated  by  the 
sharpest  angles  and  the  brightest  appearance.     If  the  coal  is  dull 
and  shows  seams  and  cracks,  it  will  split  into  small  fragments  in 
the  heat  of  the  furnace  and  will  not  prove  economical. 

(e)  Bituminous  coals  should  be  avoided  which  show  fractures 
with  whitish  films  or  rusty  stains  as  being  indications  of  the  pres- 
ence of  sulphur  and  pyrites. 

Peat  or  Turf.  This  fuel  is  obtained  from  bogs  and  similar 
places,  and  consists  of  the  woody  roots  of  plants  mixed  with  earthy 
matters.  It  contains  large  percentages  of  moisture,  and  even  when 
dried  will  remain  so  only  under  great  care.  In  some  localities  it 
is  pressed  into  blocks  or  briquettes  of  convenient  size.  Its  com- 
mercial use  is  very  limited  for  steam-raising  purposes.  When 
air-dried  it  contains  about  25  to  30  per  cent  of  moisture,  ash  from 
3  to  12  per  cent,  and  has  a  specific  gravity  of  0.4  to  0.5  in  the  ordi- 
nary state. 

Wood.  This  fuel  is  largely  used  in  certain  districts.  When 
freshly  cut  it  contains  about  40  per  cent  of  moisture,  depending 
on  the  kind.  After  being  air-dried  for  8  or  10  months  it  will  still 
contain  at  least  20  per  cent.  When  dried  it  contains  on  the  aver- 
age 50  per  cent  of  carbon  and  50  per  cent  of  oxygen,  hydrogen,  etc. 
The  specific  gravity  varies  from  about  0.3  to  1.2,  and  the  amount 
of  ash  from  0.5  to  6  per  cent.  The  lighter  varieties  burn  the  most 
readily,  while  the  denser  kinds  give  the  most  heat  and  burn 
longest. 

The  heating  power  of  one  cord  of  hard  wood  is  about  equal  to 
one  ton  of  average  anthracite;  while  one  cord  of  soft  wood  to  a 
little  less  than  half  a  ton.  The  heating  value  of  the  different 
species  is  about  the  same  when  compared  by  weight,  that  is,  one 
pound  of  hard  wood  is  about  equal  to  one  pound  of  soft  wood.  The 
heating  power  of  dry  wood  used  as  a  fuel  is  usually  assumed  as 


FUELS  37 

equal  to  0.4  that  of  average  soft  coal  of  same  weight;  that  is,  2J 
pounds  of  wood  are  equivalent  to  one  pound  of  coal. 

Coke  and  Charcoal.  These  fuels  are  made  by  evaporating  the 
volatile  constituents  from  coal  and  wood  respectively.  They  both 
give  a  very  hot  fire,  but  on  account  of  expense  are  not  used  com- 
mercially for  steam-making. 

Miscellaneous  Fuels.  Sawdust,  Straw,  Bagasse.  Sawdust  is 
a  favorite  fuel  in  sawmills  and  in  their  vicinity,  as  when  allowed 
to  collect  it  becomes  a  source  of  danger  from  fire.  It  absorbs 
moisture  very  quickly,  more  so  than  the  wood  from  which  it  was 
produced,  on  account  of  its  increased  surface.  It  has  the  same 
heating  power  as  the  original  wood.  It  requires  a  large  supply 
of  air  to  properly  consume  it,  and  therefore  the  furnace  and  com- 
bustion-chamber should  be  given  liberal  proportions. 

Straw  as  a  fuel  is  only  used  when  it  becomes  the  cheapest 
method  to  get  rid  of  it.  It  has  a  heating  power  varying  from  about 
5000  to  6000  heat-units  per  pound.  Its  combustion  is  not  unlike 
that  of  wood  shavings. 

Bagasse  or  megass  is  refuse  sugar-cane  and  is  used  as  a  fuel  on 
the  sugar-plantations.  Owing  to  the  woody  fibre,  the  sugar  and 
other  combustibles  contained,  it  gives  off  a  great  amount  of  heat. 
As  single  crushing  of  the  cane  extracts  about  66  per  cent  of  the 
sugar  juice,  and  double  crushing  about  72  per  cent,  the  green 
bagasse  consists  approximately  of: 

Single-         Double- 
crushed,        crushed. 

Woody  fibre 37%  45% 

Sugar 10  9 

Water 53  46 

When  consumed  at  a  high  temperature,  the  oxygen  contained 
is  nearly  sufficient  to  satisfy  the  carbon  and  hydrogen,  so  that  little 
surplus  air  is  required.  Under  favorable  conditions  about  1.1 
pounds  of  bagasse  are  equivalent  to  1  pound  of  Welsh  coal. 

The  furnace  *  is  constructed  of  brick,  independent  of  the  boilers, 
and  the  crushed  cane  is  continuously  fed  by  a  belt  conveyor  into 
a  hopper,  often  arranged  so  as  automatically  to  control  the  amount. 
A  form  of  bagasse  furnace  is  shown  in  Fig.  3  and  arranged  to  heat 
two  sets  of  boilers.  Another  form  of  furnace  is  shown  in  Fig.  4. 
*  See  "Megass  Furnaces,"  Proceedings,  Inst.  C.  E  ,  Vol.  167. 


38 


STEAM-BOILERS 


FIG.  3. — Bagasse  Furnace— Stillman  Type. 


FUELS 


39 


/  ooooooo 
/ oooooooo 
ro  oo 

O  oO 


\  ° 

\0 
\0 

\o 

X 


CO 

o 
0 
0 

o 
oooooo 


40  STEAM-BOILERS 

Protection  from  Weather. — All  the  solid  fuels  should  be  properly 
housed  from  the  weather.  When  exposed  they  absorb  moisture 
in  greater  or  less  amounts,  the  evaporation  of  which  causes  a  loss. 
All  the  coals,  but  especially  the  bituminous  grades,  undergo  a 
waste  when  exposed,  due  to  a  slow  absorption  of  oxygen  from, 
the  atmosphere,  which  reduces  their  heating  power.  The  saving 
by  proper  housing  may  be  more  than  offset  by  the  interest  on  the 
cost  of  a  building. 

Coals  which  contain  the  compounds  of  sulphur  and  iron  are 
liable,  especially  when  wet,  to  a  rapid  oxidation,  the  generation 
of  considerable  heat  and  finally  spontaneous  combustion.  Such 
coals  should  be  stored  in  dry  places,  well  ventilated.  This  applies 
especially  to  the  coal-bunkers  on  ships. 

Owing  to  the  large  space  required,  it  often  becomes  impossible 
to  house  wood  when  stacked  for  fuel  purposes.  The  wood  is 
usually  cut  into  "cord  lengths,"  that  is,  four  feet  long,  and  should 
be  neatly  and  evenly  piled  so  as  to  expose  the  sides  of  the  pile 
to  the  sun  as  well  as  to  have  its  direction  at  right  angles  to  the 
prevailing  winds,  in  order  that  the  air  may  pass  through  the  pile 
and  assist  in  drying.  All  the  pieces  should  be  so  laid  as  to  shed 
rain,  and  all  outside  pieces  or  slabs  be  placed  on  the  top  in  the 
nature  of  a  roofing.  The  fire-room  should  be  designed  sufficiently 
large,  so  as  to  accommodate  two  stacks  of  wood,  one  for  imme- 
diate use  and  the  other  for  drying  while  awaiting  its  turn. 

Chemical  Composition  of  Coals.  Coals  differ  widely  as  judged 
by  their  chemical  analysis.  It  is  not  within  the  scope  of  this 
work  to  treat  this  subject  fully,  but  reference  should  be  made  to 
works  on  the  subject.  Kent's  "Handbook  for  Mechanical  En- 
gineers "  gives  a  number  of  analyses  of  many  different  kinds  of 
coal. 

The  principal  difficulty  in  analyzing  coal  is  to  obtain  an  aver- 
age sample.  For  details  of  an  approved  method,  refer  to  the 
Code  of  Steam-boiler  Trials  as  adopted  by  the  American  Society 
of  Mechanical  Engineers. 

The  heating  value  may  be  calculated  by  the  Dulong  formula, 
which  with  revised  constants  is: 

Total  heat  of  combustion  =  h  =  14,600C+  62,000 /H--J  +  4000S. 


FUELS 


41 


For  the  purpose  of  illustration,  assume  ultimate  analyses  as 
follows: 


Kind  of  Fuel. 

Percentage  of 

Carbon. 

Hydrogen  . 

Oxygen. 

Ash. 

Anthracite  

93 

87 
79 
65 

1 
2 
3 
5 

1 

3 

8 
18 

5 

8 
10 
12 

Semi-anthracite  

Semi-bituminous  

Bituminous  

From  this  assumption  it  must  not  be  understood  that  the 
percentage  of  ash  recedes  from  the  anthracite  in  any  regular 
progression. 

Then  the  total  heat  of  combustion  of  such  coal  per  pound,  as 
calculated  by  the  above  formula,  would  be : 

Anthracite, 

h  =14,600X0. 93+  62,000  ^0.01-^^^  =  14,275 B.T.U. 

Semi-anthracite, 


°-03 


14,174  B.T.U. 


h  =  14,600X0.  87+  62,000  (0.02- 
Semi-bituminous, 

h  =  14,600X  0  .  79+  62,000  /0  .  03-  ^^}  =  14,014  B.T.U. 

\  o    / 

Bituminous, 

h  =  14,600X  0  .  65+  62,000  (  0  .  05-  ^?  )  =  13,985  B.T.U. 


Very  frequently  the  analysis  merely  states  the  amounts  of  fixed 
carbon,  volatile  matter  and  ash.  Such  an  analysis  is  called  the 
"proximate  analysis."  The  volatile  matter  may  be  taken  as  con- 
sisting of  marsh-gas,  or  CH4,  without  producing  a  sensible  error. 
The  total  heat  of  combustion  may  then  be  calculated  as  below. 

The  following  is  an  average  of  24  analyses  of  Pennsylvania 
anthracites,  as  stated  by  Briton: 

Fixed  carbon  ...............................   91.05% 

Volatile  matter  (CHJ  ...........  .............     3.45 

Ash  and  moisture  ............................     5  .  50 

The  volatile  matter  consists  of  (by  weight)  12C+4H  or 
JC+JH;  therefore, 


42  STEAM-BOILERS 

1X14,600X0.0345 =       377.8 

1X62,000X0.0345 =       534.7 

The    heat-units    due    to    the    combustion  of 

carbon,  14,600X0.9105 =  13,293.3 


Total  H.  U.  per  pound =  14,205.8 

In  the  proximate  analysis  the  percentage  of  moisture  should 
always  be  stated  by  itself,  and  not  be  added  to  any  quantity  such  as 
ash.  The  percentage  of  sulphur  should  also  be  stated,  but  not 
included  in  the  100  percentage,  since  the  sulphur  gives  an  indication 
of  "clin leering." 

When  moisture  is  present,  as  in  nearly  every  case,  then  the  total 
heat  of  combustion  available  is  found  by  subtracting  from  the  above 
results  the  heat  necessary  to  evaporate  this  moisture.  This  may  be 
done  by  the  following  formula: 

Heat-units  required  to  evaporate  moisture  in  one  pound  of  coal 
=  Percentage  of  moisture  divided  by  100,  multiplied  by 

{ (212  -  Ta)+  966+  0.48  (Tf-  212)}. 

In  which   Ta  denotes  temperature  of  air  in  boiler-room; 
Tf  of  furnace-gases; 

966  equals  latent  heat  of  evaporation  of  water; 
0.48    equals    specific    heat    of    steam    under    constant 
pressure. 

The  ash,  as  reported  in  analyses,  consists  of  silica,  oxide  of  iron, 
potash,  alumina,  lime,  magnesia,  soda,  barium,  phosphorus  in  phos- 
phates, sulphur  in  sulphates,  etc. 

Liquid  Fuels.  These  consist  of  the  mineral  oils,  and  their  use 
has  become  more  extended  in  the  past  few  years.  No  doubt  they 
would  have  a  still  wider  field  if  there  were  less  difficulty  in  obtaining 
a  regular  and  constant  supply. 

The  greatest  quantities  of  the  petroleum  oils  are  produced  in 
the  United  States  and  in  Russia.  Other  oil  fuels  are  blast-furnace 
oil,  shale  oil,  creosote,  green  and  similar  tar  oils. 

The  petroleum  oils  have  a  composition  approximately  as  fol- 
lows: Carbon,  86%;  hydrogen,  13%;  and  oxygen,  1%.  The 
specific  gravity  varies  from  0.80  to  0.94,  so  that  a  gallon  of  oil 
weighs  between  6.6  and  7.6  pounds. 


FUELS  43 

As  the  total  heat  of  combustion  of  a  pound  of  oil  varies  from 
about  19,000  to  22,000  heat-units,  this  fuel  has  a  theoretical  evapo- 
rative power  of  from  19.6  to  22.7  pounds  of  water  per  pound  of  oil. 

The  oil  is  fed  from  tanks,  and  blown  into  the  fire-box  or  combus- 
tion-chamber by  means  of  a  nozzle.  This  blast  induces  a  current 
of  air  which  assists  in  the  combustion,  although  an  additional  supply 
is  allowed  to  enter  at  the  bottom  of  the  furnace. 

No  grate  is  required,  although  a  grate  is  often  employed,  which 
is  covered  with  loose  fire-brick.  These  bricks  radiate  off  the  heat 
and  help  to  warm  the  air  entering  from  below.  Sometimes  a  small 
coal  fire  is  employed  to  light  the  oil-blast  in  case  the  flame  should 
be  extinguished.  Little  or  no  change  being  required  in  the  ordinary 
form  of  boiler-setting,  beyond  the  introduction  of  the  injector- 
nozzles,  renders  the  boiler  fit  for  the  use  of  coal  at  any  time  in  case 
the  oil-supply  should  be  interrupted. 

The  flames  from  the  nozzles  may  be  introduced  into  the  furnace 
in  horizontal,  diagonal  or  vertical  directions,  as  may  be  required. 

The  injector-nozzles  are  made  in  a  great  variety  of  forms,  but 
all  operate  on  the  same  principle. 

The  blast  may  be  made  by  the  employment  of  compressed  air  or 
steam.  The  latter  method  is  the  more  popular,  since  the  steam 
can  be  taken  direct  from  the  boiler,  while  the  air  necessitates  the  use 
of  a  compressor.  The  first  boiler  can  be  fired  by  a  donkey  boiler 
using  coal,  or  by  one  of  the  main  battery  being  fitted  to  use  coal  until 
the  steam-pressure  be  sufficient  to  turn  on  the  oil-blast.  The  main 
object  sought  is  to  blow  the  oil  into  the  combustion-chamber  in  the 
form  of  spray,  technically  termed  "atomizing"  or  "  pulverizing " 
the  oil.  This  pulverizing  permits  of  its  rapid  combustion,  which 
resembles  tho  burning  of  a  gas.  Fig.  5  shows  a  fuel-oil  burner  oper- 
ated by  a  steam- jet,  and  Fig.  6  one  operated  by  an  air-blast. 

The  direction  of  the  blast  should  be  such  as  to  prevent  the  flame 
from  impinging  directly  on  the  furnace-plates,  and  for  this  reason 
it  is  often  blown  against  the  pile  of  fire-brick  mentioned  above, 
sometimes  called  a  "  target." 

The  intensity  of  the  flames  is  easily  controlled  by  regulating 
the  blast,  which  in  turn  controls  the  supply  of  oil. 

Nearly  all  the  pulverizing  injector-nozzles  are  designed  ac- 
cording to  one  of  the  following  methods:  The  blast  may  enter 
at  the  centre  and  the  oil  on  the  outside,  or  the  oil  may  enter  at  the 


44 


FUELS  45 

centre  and  the  blast  on  the  outside.  Practice  has  demonstrated 
that  there  is  little  if  any  difference  in  efficiency  between  the  inside 
and  outside  methods.  Most  engineers,  however,  favor  the  blast 
being  on  the  outside  with  the  oil  at  the  centre,  since  the  blast  in 
this  position  has  the  advantage  of  inducing  a  stronger  current  of 
air;  and  further,  this  method  permits  of  the  use  of  a  circular  open- 
ing for  the  oil,  which  is  less  liable  to  clog  or  choke  up  than  the 
annular  one,  which  would  have  to  be  used  if  the  blast  were  at  the 
centre. 

Reference  is  made  to  a  paper  read  by  Col.  Soliani  entitled 
"  Liquid  Fuel  for  Marine  Purposes/'  published  in  the  Transactions 
of  the  Marine  Congress,  Chicago,  1893.  It  would  appear  from  his 
experiments  that  the  heating  capacity  of  the  crude  petroleum  oils 
is  from  1.44  to  1.60  times  that  of  average  good  coal,  even  after 
deducting  the  steam  used  to  operate  the  pulverizers,  which  steam 
amounts  to  about  4  per  cent  of  the  total  evaporation  of  the  boilers. 
With  the  best  forms  of  apparatus,  Engineer-in-Chief  George  W. 
Melville,  U.S.N.,  reports  that  this  amount  can  be  reduced  to  2 
per  cent. 

The  boilers  at  the  Chicago  World's  Fair,  1893,  were  fired  with 
crude  Ohio  oil  (petroleum),  and  the  result,  being  the  average  of  the 
daily  reports,  was: 

Consumption  of  oil  per  hour 22,792  pounds 

Water  evaporated  from  212°  F.  into  steam  at  125 

pounds,  per  pound  of  oil 14. 25  pounds 

Equivalent  evaporation  from  and  at  212°  F 14.88  pounds 

Cost  of  oil  per  hour $56. 20 

Cost  of  oil  per  boiler  horse-power  per  hour 0 . 0057 

Cost  of  labor  per  boiler  horse-power  per  hour 0 . 0006 

Cost  of  boiler  horse-power  per  hour 0 . 0063 

Experiments  were  made  by  Mr.  Holden  on  four  locomotives  of 
the  Great  Eastern  Railway  in  England  (Engineer,  15  February, 
1895).  The  engines  were  express  locomotives  of  the  same  type,  and 
the  experiments  lasted  for  eight  weeks,  1  December,  1894,  to  12 
January,  1895.  Two  of  the  engines  burned  coal,  and  two  coal  and< 
oil,  Fig.  7.  The  oil  used  was  'astatki/.  or  petroleum  refuse. 


46 


STEAM-BOILERS 


-S 


FUELS 


47 


\ 


1               f 

\i    STEAM    PIPE    FROM   BOILER  f  \ 

1   j        1  1/4  OIL  PIPE  TO        |_, 

i^^looo^ojp       \ 

I              OIL  HEATER             f 

1          ! 

jj   1 

3      1 

5          | 

8       | 

48  STEAM-BOILERS 

The  results  were : 

1  pound  of  oil  (maximum  value)  was  equivalent  to  2.4   pounds  coal 
1      "        "   "  (minimum  value)     "  "         "2.0 

1      "        "   "  (average  value)         "  "          "2.18       " 

"  In  working  *  on  Mr.  Holden's  system  a  thin  coal  fire  is  kept  on 
the  grate,  and  to  assist  in  keeping  the  grate  properly  covered  with 
a  very  thin  fire  lumps  of  chalk  are  placed  on  the  grate  when  starting 
work  for  the  day.  The  ash-pan  dampers  are  kept  very  nearly 
closed,  nearly  the  whole  of  the  air  required  for  supporting  combus- 
tion entering  either  the  injector-tubes  or  at  the  first  door,  which  is 
kept  open  and  fitted  with  an  internal  deflector  just  as  when  coal  alone 
is  being  burnt.  It  is  found  that  when  burning  the  liquid  fuel  an 
exceedingly  soft  blast  is  required,  and  the  blast-nozzle  has  to  be 
materially  larger  than  usual.  The  first  experiments  of  Mr.  Holden 
on  liquid  fuel  were  made  at  the  Stratford  shops  of  the  Great  Eastern 
Railway,  using  the  by-products  from  the  Pintsch's  oil-gas  works. 
The  arrangement  was  next  applied  to  three  boilers  of  the  loco- 
motive type  at  Stratford,  and  on  these  its  performances  have 
been  very  satisfactory.  The  boilers  are  worked  at  80  pounds 
pressure,  and  the  comparative  results  of  a  week's  working  with 
coal  only,  and  with  coal  and  liquid  fuel  in  combination,  have  been 
as  follows:  With  coal  (Staveley)  only,  the  consumption  for  63^ 
hours'  work,  including  lighting  up,  was  156  cwt.,  or  275.1  pounds 
per  hour.  With  the  coal  and  oil  in  combination  there  were  used 
in  60^  hours'  work  (including  lighting  up)  55  cwt.  Staveley  coal 
and  546  gallons  of  green  oil,  or  an  average  of  101.8  pounds  of  coal 
and  9  gallons  of  oil  per  hour.  With  coal  only,  the  evaporation 
was  at  the  rate  of  7.16  pounds  of  water  per  pound  of  coal,  while 
with  the  coal  and  oil  it  was  8.91  pounds  per  pound  of  the  com- 
bined fuel. 

"With  the  liquid  fuel  it  is  found  that  the  steam  is  kept  up 
more  easily  and  steadily  than  with  coal  alone,  while  the  liquid 
fuel  gives  especial  facilities  for  getting  up  steam  rapidly  if  required. 

"Various  kinds  of  liquid  fuel  have  been  used,  and  the  appa- 
ratus appears  capable  of  dealing  with  any  of  the  ordinary  market- 
able qualities." 

Some  of  the  oil-burning  locomotives  of  the  Southern  Pacific 
Railway  are  being  equipped  with  the  Heintzelman  and  Camp 

*  "  Liquid  Fuel  in  Locomotives,"  Engineering,  19  Oct.,  1888. 


FUELS  46 

arrangement  (Fig.  8).  The  oil  is  supplied  from  Southern  California, 
and  is  carried  in  a  tank  on  the  tender,  from  which  the  oil  can 
flow  by  gravity  to  the  atomizer.  The  novel  feature  is  the  placing 
of  the  burner  at  the  front  end  of  the  fire-box,  so  that  the  flame  is 
projected  backward.  The  air-supply  enters  at  the  bottom  near 
the  back,  and  the  products  of  combustion  have  to  pass  com- 
pletely around  the  fire-box  before  entering  the  tubes.  This  arrange- 
ment favors  complete  combustion  and  high  temperature,  and 
appears  to  work  most  satisfactorily.  It  is  found  beneficial  to 
warm  the  oil  in  a  heater  before  it  reaches  the  burner.  A  steam 
connection  also  is  arranged  to  heat  the  oil  in  the  storage  tank,  so 
as  to  warrant  the  flow  of  a  thick  oil  by  gravity  to  the  atomizer. 

A  coal  fire  is  not  required  on  the  grate  of  a  modern  oil-burning 
furnace. 

Crude  oil  was  used  as  a  fuel  at  the  San  Francisco  Midwinter 
Fair,  1894-95.  (Engineering,  1  March,  1895.)  The  burner  was  a 
central  tube  about  J  of  an  inch  in  diameter,  through  which  the  oil 
passed,  and  the  flow  was  controlled  by  a  valve.  The  steam-jet 
surrounded  this  oil- jet,  and  was  given  a  rotary  motion  by  mean?  of 
guides,  thus  more  completely  atomizing  the  oil. 

It  was  found  that  a  number  of  small  jets  were  more  eco- 
nomical than  one  large  one,  because  (1)  the  oil  was  more  per- 
fectly atomized,  (2)  the  flame  better  distributed,  and  (3)  better 
results  could  be  obtained,  when  the  boiler  was  not  being  worked  at 
full  capacity,  by  extinguishing  some  of  the  jets  and  using  the 
others  at  full  capacity,  in  place  of  throttling  all  the  jets. 

The  best  result  was  an  evaporation  of  15.13  pounds  of  water 
from  and  at  212°  F.  per  pound  of  oil,  while  the  average  was  14.3 
pounds.  The  maximum  theoretical  evaporative  power  of  the  oil 
was  20.7  pounds  of  water,  equivalent  to  a  heating  power  of  19,990 
heat-units  per  pound. 

Mr.  R.  Wallis,  in  a  paper  (Transactions  of  the  American  Society 
of  Naval  Engineers,  Vol.  IX,  p.  781)  read  before  the  Northeast 
Coast  Institution  of  Engineers  and  Shipbuilders,  England,  1897, 
states  that  the  air-blast,  if  heated,  gives  good  results,  but  that  more 
air  than  steam  is  required  and  that  they  are  more  noisy;  that  the 
air-blast  gives  a  shorter  flame  and  a  more  intense  heat  for  a  shorter 
distance  from  the  flame.  That  the  danger  of  an  explosion  of  oil-gas 
in  the  combustion-chamber  when  lighting  up,  especially  if  the  blast 
has  been  stopped  for  a  short  time  only,  is  very  much  greater  with  air 


50 


STEAM-BOILERS 


than  with  steam.  That  there  appears  to  be  a  better  economy  with 
steam-blasts,  even  including  the  water  lost  in  the  atomizer.  That 
there  is  less  liability  of  a  breakdown  with  steam,  since  the  air  sys- 
tem is  complicated  by  the  compressor.  That  the  greatest  danger  of 
explosion  of  oil-gas  and  consequent  backflash  from  the  furnace  doors 
is  in  the  relighting  after  the  flames  have  been  extinguished  but  a 
short  time.  That  any  small  leakage  of  oil  finding  its  way  into  the 
heated  furnace  gasifies  and  forms  an  explosive  mixture  with  the 
air,  and,  if  the  lighting-up  torch  be  introduced  under  these  condi- 
tions, an  explosion  may  result,  with  possible  injury  to  the  person 
holding  the  torch.  That  before  lighting  a  furnace  it  should  be  well 
blown  through  with  steam.  That  the  steam- jets  should  be  opened 
first,  then  the  torch  inserted,  and  finally  the  oil  turned  on.  That 
there  is  no  risk,  even  with  the  use  of  oil  fuels  having  low  flash-points, 
when  these  precautions  are  taken.  That  the  average  of  a  number 
of  experiments,  using  the  Rusden  and  Eeles'  sprayer,  gave  the 
following  heat-balance;  the  fuel  being  Russian  astatki  and  the 
weight  of  steam  required  to  spray  one  pound  of  oil  being  0.3  lb.: 


Heat-balance. 

Heat-units. 

Equivalent 
Evaporation 
from  and  at 
212°  F. 

Total  heat  of  combustion  of  1  pound 
Carbon  087X14500 

of  oil  : 

12,615 
7,444 

20.7 
3.0 

Hydrogen  0  12X62  032 

Heat  in  waste  gases  at  450°  F.  : 
Carbonic  acid  gas 

3.19  pounds 
0.72       " 
1.08       " 
0.30       " 
2.78       " 

nee 

20,059 

269 
909 
1,452 
29 
257 

Nitrogen                                              ] 

Water  vapor  from  combustion.  .  . 
"          "         "     sprayer         .    . 

Surplus  air  taken  at  20%  

Heat  lost  by  radiation,  etc.,  by  differe 
Heat  absorbed  by  water  in  boiler 

2,916 

17,143 

1,687 

.17.7 

1.7 

15,456 

16.0 

That,  from  a  study  of  the  annexed  table,  the  heating  value  of 
the  oil  is  about  1J  times  that  of  coal,  but  practice  has  repeatedly 
shown  that  oil  fuel  is  equivalent  in  evaporative  power  to  twice  its 
weight  of  coal.  That  this  difference  can  be  accounted  for  to  a  great 
extent,  as  follows : 


FUELS 


51 


1.  The  combustion  of  the  liquid  fuel  is  complete,  whereas  that  of 
coal  is  not,  consequently  in  the  former  case  there  is  no  lost  heat  in 
smoke  or  soot. 

2.  There  are  no  ashes  or  clinkers,  and  consequently  no  fires  to 
clean  with  the  accompanying  loss  of  heat  and  drop  in  the  steam- 
pressure. 

3.  The  boiler-tubes  are  always  free  from  soot  and  clean,  and 
therefore  always  in  the  best  condition  for  transmitting  the  heat 
from  the  gases  passing  through  them  to  the  water  of  the  boiler. 

TABLE  VIII 

COMPOSITION    OF    FUEL-OILS 


Fuel. 

O 

GQ 

Chemical  Composition. 

H 
PQ 

1   • 

M 

fe  3 

Theoretical 
Evapora- 
tion. 

.a-s 

c  a 
•Z  ri 
2 

|2 

£ 

1-|| 

Carbon, 
Per  Ceni 

|| 

c  S 

,c 

is 

6 

!* 

02 

&.« 
s* 

i* 

^S 

0>  O. 

H 

Petroleum  : 
Penn.  heavy  crude  
Caucasian  light  crude.  .  . 
heavy  crude  . 
refuse  
Crude,  avg.  15  samples  . 
Refined,  average  
Scotch  blast-furnace  oil  . 
Coal: 
Avg.  98  samples,  British. 

0.886 
0.884 
0.938 
0.928 
0.870 
0  .  760 
0.920 

1.279 

84.9 
86.3 
86.6 
87.1 
84.7 
72.6 
83.6 

80.4 

13.7 
13.6 
12.3 
11.7 
13.1 
27.4 
10.6 

5.2 

1.4 
0.1 
1.1 
1.2 
2.2 

9^4 

7.87 

4.0 

20,736 
22,027 
20,138 
19,832 
20,233 
27,531 
18,590 

13,968 

21.48 
22.79 
20.85 
20.53 
20.94 
28.50 
19.20 

14.46 

14.56 
14.74 
14.28 
14.12 
14.29 
17.93 
17.93 

11.34 

16.0 
8.13 

1.2 

o.i 

1.25 

4.  The  temperature  of  the  escaping  gases  may  be  considerably 
lower  than  is  required  to  create  the  necessary  draft  for  coal-firing. 

5.  The  admission  of  air  being  under  complete  control,  and  the 
fuel  being  burned  in  fine  particles  in  close  contact  with  the  oxygen 
of  the  air,  only  a  small  excess  of  air  above  that  actually  necessary 
for  the  complete  combustion  of  the  fuel  is  required.     With  coal,  in 
order  to  insure  as  complete  combustion  as  possible,  a  very  much 
larger  excess  of  air  is  required.* 

*  Passed  Assistant  Engineer  John  R.  Edwards,  U.S.N.,  delivered  a  lec- 
ture on  "Liquid  Fuel  for  Naval  Purposes"  before  the  Naval  War  College 
which  contained  much  of  value.  (See  Transactions  American  Society  Naval 
Engineers,  Vol.  VII,  p.  744.)  The  Pennsylvania  Railroad  made  a  number 
of  experiments  with  oil  fuels  which  were  reported  to  be  very  satisfactory. 
The  U.  S.  Navy  Department  has  made  a  series  of  experiments  and  obtained 
very  complete  data,  see  Report  of  Liquid  Fuel  Board,  U.  S.  Navy,  pub- 
lished in  Journal  Am.  Soc.  Naval  Engineers,  August  1904. 


52  STEAM-BOILERS 

The  direction  of  the  jet — horizontal,  diagonal  or  vertical — does 
not  appear  to  make  any  marked  difference  in  efficiency.  As  a 
matter  of  convenience  the  horizontal  direction  seems  best,  since  the 
nozzles  can  be  made  to  pass  through  the  ordinary  fire-door  opening 
or  through  the  front  casing,  and  necessitate  no  other  change  except 
that  of  the  door.  As  the  grate  is  undisturbed,  a  return  to  coal  at 
any  tune  is  an  easy  matter. 

A  considerable  economy  is  effected  when  the  air-supply  is  heated 
before  its  mixture  with  the  oil.  This  can  be  done  by  the  escaping 
gases,  the  air  being  drawn  through  a  pipe  coil  placed  at  the  base  of 
the  flue.  The  air-supply  pipe  should  be  large,  so  as  not  to  create 
loss  by  friction  due  to  a  high  velocity  through  it. 

The  oil-tank  should  be  located  so  that  the  fuel  can  readily 
flow  to  the  nozzles,  but  should  be  lower  than  the  burners  to  prevent 
accident  from  flooding.  The  oil  can  be  drawn  to  the  atomizers 
by  the  suction  of  the  blast,  but  is  generally  pumped  to  positively 
control  the  supply  and  maintain  a  constant  pressure.  The  oil 
can  be  burned  with  a  natural  or  an  artificial  draft.* 

There  is  no  doubt  that  liquid  fuel  would  be  used  to  a  much 
greater  extent  if-  the  supply  could  be  depended  upon.  In  localities 
where  it  is  cheap  it  is  of  great  value  as  a  fuel,  but  in  most  places  its 
uncertain  delivery  and  cost  are  prohibitive.  For  use  in  reheating 
and  in  heating  furnaces  for  bending  structural  shapes  and  plates, 
as  well  as  in  annealing  furnaces,  its  uniform  heating  power  has 
created  for  it  a  marked  value. 

When  compared  with  good  coal  the  commercial  efficiency  of 
liquid  fuel  can  be  rated  at  1  pound  of  oil  to  from  1.6  to  2  pounds  of 
coal,  which  will  include  all  the  advantages  due  to  the  oil;  so  that  at 
equal  cost  the  oil  can  be  preferred,  due  to  its  cleanliness.  Good  fuel- 
oils  will  evaporate  from,  say,  16  to  17  pounds  of  water  from  and  at 
212°  F.  per  pound. 

For  the  purpose  of  illustration  assume : 

Weight  per  gallon  of  fuel-oil,  pounds 6.8 

Cost  per  barrel  of  42  gallons  delivered $0 . 94 

Then, 

The  cost  of  2000  pounds  of  fuel-oil  would  be $6. 58 

*For  use  of  retarders  with  liquid  fuel,  see  page  192. 


FUELS  53 

Therefore,  at  a  commercial  efficiency  of  one  to  two,  the  values  of 
the  fuels  are  equal  when  the  price  of  the  coal  delivered  is  $3.29  per 
ton.  This  should  include  the  cost  of  removal  of  ashes  from  the  coal. 

The  advantages  of  liquid  fuel  are : 

1.  Reduction  in  number  of  firemen  in  proportion  of  5  or  6  to  1. 

2.  Easy  lighting  of  fires  and  more  regular  supply  of  heat. 

3.  The  fires  can  be  readily  regulated  to  suit  the  demand  for 
steam,  and  can  be  promptly  extinguished. 

4.  The  small  proportion  of  refuse  or  ash  and  its  easy  disposal. 

5.  The  storage-tanks  can  be  located  to  best  advantage,  while 
coal-bins  must  be  near  the  boilers. 

The  disadvantages  may  be  stated  as: 

1.  Danger  from  explosion  and  fire  due  to  the  vapors  from  the 
storage-tanks. 

2.  Loss  due  to  evaporation. 

3.  The  unpleasant  odor. 

Gaseous  Fuels.  These  fuels  have  practically  the  same  advan- 
tages and  disadvantages  as  the  liquid  fuels,  and  like  them  afford  a 
clean  fire-room.  In  some  special  cases  gas  is  purposely  made  for 
use  as  a  fuel,  but  the  general  introduction  of  artificial  gas  for  steam- 
generating  is  prohibited  by  its  cost. 

The  waste  gases  from  some  metallurgical  operations  are  used  for 
heating  steam-boilers.  The  gases  are  simply  conveyed  in  a  large 
pipe  or  flue,  while  at  high  temperature,  beneath  the  battery  of  boil- 
ers, and  there  supplied  with  the  requisite  air  to  complete  the  com- 
bustion. 

The  natural  gases  are  by  far  the  most  common  of  the  gaseous 
fuels,  and  in  the  localities  where  found  are  used  with  great  economy. 

From  whatever  source,  the  gas  is  carried  to  the  furnace  in  pipes, 
and  ignited.  The  burner  may  be  of  any  convenient  shape,  but 
usually  is  a  plain  tapered  mouthpiece.  Some  of  the  best  gas- 
burners  are  designed  on  the  principle  of  the  Bunsen  burner,  so  as 
to  insure  more  perfect  combustion  and  a  hotter  flame.  The  flame 
may  be  horizontal,  vertical  or  diagonal,  to  suit  the  situation,  but  it 
4s  best  not  to  let  it  play  directly  against  the  furnace-sheets.  As 
with  oil,  the  grate  may  be  covered  with  loose  fire-bricks,  which  will 
greatly  assist  in  warming  the  air-supply  as  it  passes  between  them. 
If  the  grates  are  left  in  place,  return  can  alwrays  be  made  to  coal  in 
cases  of  emergency.  Sometimes  a  small  coal  fire  is  maintained  on 


54 


STEAM-BOILERS 


the  grate,  so  as  to  relight  the  gas  should  it  become  extinguished 
accidentally. 

The  gas  in  the  supply-main  is  under  a  pressure  varying  from  1 
to  8  oz.,  equivalent  to  1^  to  12  inches  of  water.  When  the  gas- 
pressure  exceeds  8  ounces  it  is  usual  to  use  a  reducing- valve.  A 
high  pressure  is  apt  to  be  wasteful  as  well  as  dangerous  from  ex- 
plosions, and  a  reduced  pressure  is  generally  required  by  the  fire 
insurance  companies. 

It  has  been  found  that  one  fireman  can  attend  to  boilers  furnish- 
ing 200  H.P.  with  coal  as  a  fuel;  while  with  gas-firing  one  man  can 
manage  1500  H.P.;  so  that  the  reduction  in  labor  is  about  7J  to  1 
in  large  plants. 

The  heating  powers  of  the  gaseous  fuels  vary  through  wide  limits. 
About  26,000  feet  of  natural  gas  or  100,000  feet  of  lean  producer- 
gas  are  equivalent  to  one  ton  of  good  average  coal. 

The  following  tables,  copied  from  Kent's  "  Mechanical  Engineer's 
Pocket-book,"  are  self-explanatory.  Table  IX  may  be  considered 
as  an  average  for  the  several  gases,  the  figures  being  volumetric 
percentages;  and  Table  X  gives  E.  P.  Reichhelm's  experience,  who 
states  that  under  ordinary  conditions  in  furnaces  for  drop-forging, 
annealing-ovens,  and  melting-furnaces  for  brass,  copper,  etc.,  the 
loss  due  to  draft,  radiation  and  the  heating  of  space  not  occupied 
by  the  work  is  with  gas  of  fair  to  good  quality  about  25  per  cent. 

TABLE  IX 

COMPOSITION    OF    FUEL-GASES 


Natural 
Gas. 

Coal- 
gas. 

Water- 
gas. 

Producer-gas. 

Anthra- 
cite. 

Bitumi- 
nous. 

27.0 
12.0 
2.5 
0.4 
2.5 
56.2 
0.3 

65.6 
156,917 

CO 

0.50 
2.18 
92.60 
0.31 
0.26 
3.61 
0.34 

6.0 
46.0 
40.0 
4.0 
0.5 
1.5 
0.5 
1.5 
32.0 
735,000 

45.0 
45.0 
2.0 

i!6 

2.0 
0.5 
1.5 
45.6 
322,000 

27.0 
12.0 
1.2 

"2.5" 

57.0 
0.3 

65.6 
137,455 

H                               

CH4                

C,H, 

CO,  

N              

O                

Vapor  

Weight  in  pounds  of  1000  cu.  ft  . 
Heat-units  in  1000  cubic  feet.  .  . 

45.60 
1,100,000 

FUELS 


55 


TABLE  X 

FUEL   VALUES    OF    GASES 


Kind  of  Gas. 

No.  of 
Heat-units 
in  1000 
Cubic  Feet 
Used. 

No.  of 
Heat-units 
in  Fur- 
naces 
after  De- 
ducting 
25%  Loss. 

Average 
Cost 
per  1000 
Cubic 
Feet. 

Cost  of 
1,000,000 
Heat-units 
Obtained 
iii  Fur- 
naces. 

Natural  gas  

1,000,000 
675,000 
646,000 
690,000 
313,000 
377,000 
185,000 
150,000 
306,365 
its  utilized 
er  1,000,OC 

750,000 
506,250 
484,500 
517,500 
234,750 
282,750 
138,750 
112,500 
229,774 

$1.25 
1.00 
0.90 
0.40 
0.45 
0.20 
0.15 
0.15 

$2.46 
2.06 
1.73 
1.70 
1.59 
1.44 
1.33 
0.65 
0.73 
0.73 

Coal-gas,  20  candle-power.  .  . 

Carburet/ted  water-gas  

Gasoline-gas,  20  candle-power  

Water-gas  from  coke  

Water-gas  from  bituminous  coal  .... 
WTater-gas  and  producer-gas  mixed  .  . 
Producer-gas  

Naphtha-gas,  fuel  1\  gals,  per  1000  ft  . 
Coal  $4  per  ton,  per  1,000,000  heat-un 
Crude  petroleum,  3  cents  per  gallon,  p 

0  heat-un 

its. 

CHAPTER  IV 
FURNACE     TEMPERATURE    AND    EFFICIENCY    OF    BOILER 

The  Temperature.  Color  Test.  Rankine's  Method  for  Calculating.  Dis- 
sipation of  Heat  Generated.  Percentage  of  Heat  Utilized.  Results.  Evapo- 
ration per  Pound  of  Fuel  and  of  Combustible.  Practical  Efficiencies. 

The  temperature  obtained  in  a  boiler-furnace  depends  on  many 
conditions,  including  the  design,  fuel,  moisture,  amount  of  air  sup- 
plied and  rate  of  combustion. 

The  temperature  can  be  measured  by  a  pyrometer;  by  observing 
the  melting  or  non-melting  of  substances,  as  specially  made  alloys; 
the  increase  in  temperature  of  a  given  weight  of  water,  when  a  block 
of  metal  of  known  weight  is  taken  from  the  furnace  and  suddenly 
immersed;  and  from  the  color. 

The  color  test  must  always  be  approximate,  as  so  much  de- 
pends on  the  eye  of  the  observer  and  the  darkness  in  which  the 
bright  object  is  viewed.  The  temperatures,  as  indicated  by  color, 
are  usually  thus  stated: 

Faint  red 960°  F. 

Bright  red 1300 

Faint  cherry 1500 

Bright  cherry 1600 

Dull  orange 2000 

Bright  orange 2200 

White  heat 2400 

Dazzling  white.  . 2700  and  over. 

Professor  Rankine's  method  of  calculating  the  hypothetical 
temperature  of  the  furnace  is  stated  in  the  formula 

WxKpXTf=h;  therefore  7>=  jp^g- , 

56 


FURNACE  TEMPERATURE  AND  EFFICIENCY  OF   BOILER     57 

in  which  W  denotes  the  weight  of  the  products  of  combustion  in 

pounds  per  pound  of  fuel  ; 
Kp  denotes  the  specific  heat  of  the  products  of  combustion 

under  constant  pressure; 
h  denotes  the  heat-units  due  to  the  combustion  of  one 

pound   of  the   fuel;    and 
Tf  denotes  the  temperature  of  the  furnace  in  degrees 

Fahrenheit  above  that  of  the  air. 

The  values  of  K  under  constant  pressure  are  : 

Carbonic  acid  .....   0.  217          Air  ..............   0.  237 

Steam  ...........   0.480          Ashes,  probably.  .  .   0.200 

Nitrogen  .........   0  .  244          Average  value  ....  0  .  237 

Assuming  that  a  good  average  sample  of  anthracite  coal  contains 
13,000  heat-units  per  pound,  then  the  furnace  temperature  above 
that  of  the  entering  air  would  be: 

With  no  excess  of  air 

13,000 


- 


13X0.237 


Note.  —  One  pound  of  fuel  plus  12  pounds  of  air  equals  13  pounds 
of  products  of  combustion. 

With  one-half  quantity  of  air  in  excess 


With  whole  quantity  of  air  in  excess 

_     13,000    _  01  0.10  T? 
^"25X0.237" 

These  temperatures  should  be  corrected  for  moisture,  when 
present,  by  deducting  the  heat  required  to  evaporate  it  into  steam. 
The  assumption  also  is  made  that  the  specific  heat  remains  constant, 
which  may  not  be  true  for  these  high  temperatures;  and  if  it  in- 
creases, the  resulting  temperatures  will  be  correspondingly  reduced. 
Such  high  temperatures  as  indicated  above  are  not  reached  in 
practice,  since  the  combustion  is  not  instantaneous,  is  not  all  com- 
pleted in  the  furnace  as  the  flame  and  gases  carry  for  some  distance, 
and  since  the  heat  is  being  continually  absorbed  by  the  boiler. 


58  STEAM-BOILERS 

The  average  temperature  immediately  over  the  fire  varies  from 
about  1400°  F.  to  1800°  F.  with  natural  drafts. 

The  quantity  of  heat  generated  in  a  boiler-furnace  is  dissipated 
in  three  ways:  that  utilized  in  the  evaporation  of  water;  that  pass- 
ing up  the  stack  with  the  waste  gases,  thus  supporting  the  draft; 
and  that  lost  by  radiation.  From  a  well-designed  boiler,  properly 
set,  the  radiation  loss  is  always  small,  being  usually  less  than  5  per 
cent.  The  heat  of  the  gases  passing  up  the  stack  is  necessarily  lost 
for  evaporation  effects,  but  is  essential  to  maintain  the  draft,  unless 
an  artificial  draft  be  provided.  The  heat  thus  carried  away  in 
the  gases  must  a*lways  be  a  considerable  proportion  of  the  total 
heat  generated. 

The  percentage  of  heat  utilized,  that  is,  the  efficiency  of  the 
furnace,  may  be  determined  thus: 

Let  Tf  denote  the  temperature  of  the  furnace; 
"    Tc       "        "  "  "    "   chimney-gases; 

"    Ta       "        "  "  "    "   air. 


Neglecting  the  loss  by  radiation  as  being  small,  then  approximately 
the  heat  utilized,  in  per  cent,  —hu=  100; 


Tf-Tc 


Tf-Ta' 

As  an  example,  assume  Tc  to  be  600°  F.;  Ta,  60°  F.;  and  the 
values  and  conditions  for  Tf  just  given. 

For  no  excess  of  air,  7>= 4219 +  60  =  4279: 

hu  =  87.1%  of  furnace  heat. 
For  one-half  air  in  excess,  7>=  2886 +  60  =  2946: 

^«  =  81.2%  of  furnace  heat. 
For  whole  quantity  of  air  in  excess,  Tf=  2194  +  60  =  2254: 

hu  =  75.3%  of  furnace  heat. 

These  results  clearly  indicate  that  (1)  the  heat  utilized  de- 
creases as  the  quantity  of  air  admitted  increases,  but  it  is  necessary 
to  have  some  excess  of  air  in  order  to  burn  perfectly  all  the  carbon 
and  hydrogen;  (2)  the  heat  utilized  increases  as  the  temperature 
of  the  chimney-gases  decreases,  and  there  should  be  sufficient 
heating  surface  to  cool  the  gases  as  much  as  possible  before  they 
escape,  although  enough  heat  must  be  left  to  create  a  draft  in 


FURNACE  TEMPERATURE  AND   EFFICIENCY  OF  BOILER    59 

order  to  burn  the  fuel;  and  (3)  the  heat  utilized  increases  as  the 
temperature  of  the  air  admitted  increases,  so  that  it  will  be  beneficial 
to  heat  the  air  before  admission  if  it  can  be  done  without  robbing 
the  furnace  of  heat  or  the  chimney  of  draft. 

Economies  of  from  5  per  cent  to  15  per  cent  have  been  obtained 
by  heating  the  air-supply  before  its  admission  to  the  furnace. 
When  mechanical  draft  is  used,  this  heating  is  often  done  by  passing 
the  air  through  conduits  warmed  by  the  escaping  gases,  the  heat  of 
which  is  not  required  in  such  cases  for  the  maintenance  of  the  draft. 
For  the  same  reason,  boilers  show  a  slightly  better  rate  of  evapora- 
tion in  summer  than  in  winter.  Some  engineers  have  taken  the 
air-supply  from  the  engine-room,  which  utilizes  part  of  the  heat 
lost  by  radiation  as  well  as  assisting  the  ventilation. 

If  no  losses  occurred  and  all  the  heat  were  available  for  evapora- 
tion, then  one  pound  of  the  best  coal,  containing,  for  example, 
15,000  heat-units  per  pound,  could  evaporate  from  and  at  212°  F. 
(15,000  divided  by  966)  15.5  pounds  of  water. 

As  in  practice  losses  must  exist,  this  result  never  can  be  obtained. 

For  sake  of  illustration,  assume  conditions  to  exist  as  before 
mentioned,  with  air-supply  twice  that  theoretically  required  for 
complete  combustion.  Neglecting  radiation  losses,  the  available 
heat  is  then  75.3  per  cent.  The  heat-units  utilized  per  pound  of 
coal  burned  would  be  13,000X0.753  =  9789.* 

Assume  that  the  boiler  is  generating  steam  at  85.3  pounds  by 
the  gauge,  and  that  the  feed-water  has  a  temperature  of  100°  F. 
Then  the  total  heat  of  evaporation  would  be,  in  heat-units  per 
pound : 

From  the  Steam-table,  1181.8- (100- 32)  =  1113.8,  or  by 
Kegnault's  Formula,  should  a  table  not  be  at  hand, 

h2>L  =  1091.7+  0.305  (327.6-  32)-  (100-  32)  =  1113.8. 

The  evaporation,  then,  of  one  pound  of  coal  under  these  con- 
ditions would  be: 

Heat-units  per  pound  of  coal        9789          _0  ,      , 

— T—  ,    .  ,     -  =  1119  Q  =  8.78  pounds  of  water. 

Heat-units  per  pound  ol  steam     1 1  lo .  8 

*  Results  calculated  in  this  manner  are  greater  than  would  occur  in  prac- 
tice, as  nearly  always  there  is  some  moisture  present.  Furthermore,  it  is 
based  on  a  constant  specific  heat,  which  may  not  be  true  for  high  tempera- 
tures as  was  mentioned  above. 


60  STEAM-BOILERS 

Multiply  this  result  by  the  factor  of  evaporation  to  find  the 
equivalent  evaporation  from  and  at  212°.  The  factor  for  the  case 
is  1.153. 

Equivalent  evaporation  from  and  at  212°  =  8.78X  1.153  =  10.12 
pounds. 

The  following  are  the  result  of  three  tests,  the  first  from  Trans- 
actions Am.  Soc.  M.  E.  1891,  page  990,  and  the  others  from  the 
author's  note-book : 

1.  Type  of  boiler Return  tubular 

Average  steam-pressure 90  pounds 

Feed-water  temperature 147°  to  150°  F. 

Evaporation   from   and   at   212°,    with 

pea  coal 9.9  pounds 

Evaporation   from    and    at   212°,    with 

anthracite  lumps 10.2  pounds 

2.  Type  of  boiler Return  tubular 

Average  steam-pressure 34.7  pounds 

Feed-water  temperature 52.5°  F. 

Coal Cross  Creek  anthracite 

Evaporation  from  and  at  212° 7.8  pounds 

3.  Type  of  boiler Return  tubular  with  superheater 

Evaporation  from  and  at  212° 8.5,  9.4,  8.9  pounds  under  vary- 
ing conditions 

Locomotives  evaporate,  when  in  clean  condition,  about  6  to  7 
pounds  of  water  per  pound  of  coal. 

The  rate  of  evaporation  is  frequently  expressed  "per  pound  of 
combustible"  in  place  of  "per  pound  of  fuel." 

"  By  fuel "  is  meant  the  fuel  as  fed  into  the  furnace,  and,  so  to 
speak,  the  term  is  used  in  the  gross  sense. 

"  By  combustible  "  is  meant  the  net  fuel,  or  that  which  is  con- 
sumed on  the  grate.  It  is  the  difference  between  the  weight  of  fuel 
as  fed  into  the  furnace  and  the  weight  of  the  refuse  as  removed. 
This  refuse  consists  of  ashes,  fuel  that  falls  into  ash-pit  through 
grate-bars,  and  the  dust  or  soot  that  may  pass  through  the  boiler 
into  the  stack.  Owing  to  the  difficulty  of  weighing  the  latter,  it 
is  seldom  considered  except  in  a  few  very  elaborate  boiler  tests. 

The  efficiency  of  the  boiler,  that  is,  the  percentage  of  the  total 
heat  of  combustion  which  is  utilized  for  evaporation,  varies  con- 
siderably.* Some  boilers  show  an  efficiency  of  less  than  50  per  cent, 

*  George  H.  Barrus'  work  entitled  "Boiler  Tests"  will  be  found  valuable 


FURNACE  TEMPERATURE  AND  EFFICIENCY  OF  BOILER    61 

but  such  low  results  are  rather  exceptional,  being  traceable  to  small- 
ness  of  size  or  to  poor  design  or  setting.  Under  ordinary  conditions 
of  practice,  efficiencies  from  50  per  cent  to  70  per  cent  may  be  con- 
sidered as  poor  to  fair;  from  70  per  cent  to  75  per  cent  as  good;  and 
over  75  per  cent  as  excellent. 

The  efficiency  of  a  boiler  can  be  determined  for  any  condition  of 
operation,  by  measuring  the  water  evaporated  and  the  fuel  burned 
during  the  same  time. 

Then  the  efficiency  in  per  cent  is; 

Heat  absorbed  by  the  water ^  = 

Heat  of  combustion  of  the  dry  fuel 

Total  heat  of  evaporation  X  rate  of  evaporation 
Heat  of  combustion  of  1  pound  of  dry  fuel 

The  above  result  is  really  the  efficiency  of  the  boiler  and  grate. 
The  efficiency  of  the  boiler,  without  the  effect  of  the  grate,  in 
per  cent  is: 

Heat  absorbed  by  the  water  _ 

•  /\  1UU  — 


Heat  of  combustion  of  the  combustible 

Total  heat  of  evaporation  X  rate  of  evaporation 

per  pound  of  combustible 
Heat  of  combustion  of  1  pound  of  combustible 

This  latter  result  omits  from  consideration  the  fuel  lost  through 
the  grate  in  an  unburned  condition,  and  should  be  the  one  used 
as  the  standard  of  comparison  for  boiler  trials.  The  word  "com- 
bustible "  is  here  used  to  mean  the  fuel  without  moisture  and  ash. 

for  reference  in  this  particular,  as  it  contains  records  of  tests  on  many  differ- 
ent types  under  variable  conditions 


CHAPTER  V 
BOILERS  AND  STEAM-GENERATORS 

General  Conditions.  Classification.  Horse-power.  Centennial  Standard. 
Am.  Soc.  M.  E.  Standard.  Heating  Surface.  Ratio  of  Heating  to  Grate 
Surface.  Evaporation  per  Square  Foot  of  Heating  Surface.  Design.  De- 
scription of  Certain  Boilers.  Proportioning  a  Boiler  to  Perform  a  Given 
Duty.  Steam-space.  Priming.  Water  Surface. 

Steam-boilers  and  Steam-generators  are  essentially  metallic 
vessels  in  which  water  is  heated  and  converted  into  steam.  The 
term  "  boiler  "  is  generic,  but  when  used  in  its  restricted  sense  it 
refers  to  those  boilers  which  are  more  properly  "  metallic  vessels  " 
in  which  there  is  a  considerable  mass  of  water  in  relation  to  the 
capacity.  On  the  other  hand,  "  steam-generator "  is  the  term 
made  applicable  to  that  class  in  which  the  mass  of  water  is  rela- 
tively small  to  the  capacity,  and  confined  principally  by  tubes 
and  parts  of  small  dimensions. 

Since  the  cost  of  fuel,  no  matter  what  kind  may  be  used,  forms 
so  great  a  proportion  of  the  total  cost  of  the  output  or  product  of 
every  plant,  it  is  all-important  that  the  boiler  be  economical  and 
efficient.  The  greatest  care  should  be  given  to*the  design  or  the 
selection  of  a  boiler  for  each  particular  case.  The  fuel  should  be 
burned  to  best  advantage,  so  as  to  generate  the  greatest  furnace 
temperature;  and  the  boiler  should  be  so  arranged  as  to  abstract 
this  heat  from  the  products  of  combustion,  permitting  no  more  to 
escape  than  may  be  necessary  for  the  maintenance  of  the  draft. 
The  gases  and  air  should  be  thoroughly  mixed  by  means  of  bridge 
walls  or  other  devices;  and  generous  proportions  should  be  given 
to  the  combustion-chamber  in  order  that  the  combustion  may  be 
completed  before  the  gases  become  cooled  by  contact  with  the  boiler 
surfaces.  In  order  to  absorb  the  heat  of  the  products  of  combus- 
tion there  should  be  plenty  of  heating  surface,  the  arrangement  of 
which  should  be  such  as  to  encourage  the  proper  circulation  of  the 

62 


BOILERS  AND  STEAM-GENERATORS  63 

water  in  the  boiler,  and  at  the  same  time  to  prevent  the  gases  from 
making  a  short  passage  to  the  stack.  While  making  the  provision 
for  the  gases  to  reach  every  portion  of  the  heating  surface,  care 
must  be  exercised  lest  too  great  a  resistance  to  draft  be  created. 
The  surfaces  from  which  radiation  may  occur  should  be  well  lagged 
or  clothed. 

The  history  of  the  steam-boiler  shows  that  the  gradual  develop- 
ment has  been  in  the  direction  of  increase  of  heating  surface,  reduc- 
tion in  weight  and  higher  pressures.  Future  improvement  no 
doubt  will  follow  these  tendencies. 

It  can  be  frankly  stated  that  there  is  no  "  best "  type  of  boiler, 
although  one  kind  may  be  much  better  suited  than  another  for 
some  particular  class  of  work,  or  for  operation  under  certain  fixed 
conditions. 

Boilers  are  usually  classified  as  being  either 

Externally  fired  or 
Internally  fired. 

The  distinctive  feature  is  whether  the  fire  on  the  grate  is  external 
to  the  boiler  proper,  as,  for  example,  the  plain  cylindrical  boiler  or 
the  horizontal  return-tubular  boiler;  or  whether  the  fire  is  internal, 
as  in  the  Scotch  boiler  or  in  the  Lancashire  boiler.  There  are  some 
types  which  are  more  or  less  difficult  to  place  under  either  head,  but 
which  belong  in  part  to  both. 
Another  classification  is 

Fire  Tubular  or 
Water  Tubular. 

The  distinctive  feature  under  these  headings  is  the  use  of  the 
tubes  or  flues.  If  the  hot  gases  pass  through  them,  the  water  being 
on  the  outside,  the  boiler  is  said  to  be  of  the  fire-tubular  type.  If 
the  water  be  in  the  tube  with  the  hot  gases  on  the  outside,  then 
the  boiler  is  water-tubular. 

As  before,  these  names  do  not  cover  all  types  for  some  boilers, 
as  the  plain  cylindrical,  have  no  tubes ;  and  again  there  are  boilers, 
known  as  " compound"  boilers,  which  are  a  combination  of  the  two 
classes. 

Horse-power  of  Boilers.  For  the  sake  of  convenience  it  has 
become  necessary  to  adopt  a  rating  for  boilers,  and  custom  has 
adopted  the  term  "  horse-power  "  to  designate  the  unit  of  compari- 


64  STEAM-BOILERS 

son.  Strictly  speaking  a  horse-power  is  the  unit  of  rate  of  work, 
and  its  application  to  the  boiler  is  a  misuse  of  the  expression,  since 
a  boiler  does  not  perform  work  in  the  sense  of  "  overcoming  of  resist- 
ance through  space."  The  term  has  become  so  general,  however, 
that  it  must  be  retained,  and  if  clearly  understood  is  as  good  as  any 
other.  It  is  to  be  urged  that  when  used  the  term  should  always  be 
"  boiler  horse-power,"  as  then  there  is  little  likelihood  of  its  being 
misinterpreted.  The  horse-power  of  an  engine  has  no  relation 
whatever  to  the  boiler  horse-power  of  the  boilers  furnishing  the 
steam. 

The  builders  of  steam-boilers  usually  rate  their  boilers  at  one 
boiler  horse-power  to  every  ten,  twelve  and  one-half  or  fifteen 
square  feet  of  heating  surface.  Such  ratings  give  little  idea  of  the 
boiler,  as  so  much  depends  on  arrangement  of  surface,  rate  of  com- 
bustion and  the  like.  While  ten  to  fifteen  square  feet  of  heating 
surface  may  correspond  to  the  average  engine  horse-power,  it  must 
not  be  forgotten  that  an  engine  horse-power  is  often  developed  on 
three  square  feet  and  even  less.  A  far  better  plan  is  to  rate  the 
boiler  according  to  the  quantity  of  water  that  it  will  evaporate. 

The  " Centennial"  standard,  being  that  used  by  the  Committee 
at  the  Exposition  in  Philadelphia,  1876,  was  an  assumption  of  30 
pounds  of  water  evaporated  per  hour  from  feed-water  at  100°  F. 
into  dry  steam  at  70  pounds  pressure  by  the  gauge,  as  being  one 
boiler  horse-power. 

The  American  Society  of  Mechanical  Engineers'  standard  is 
practically  the  same,  being  34J  pounds  of  water  evaporated  per 
hour  from  a  feed-water  temperature  of  212°  F.  into  dry  steam  at  the 
same  temperature.  The  evaporation  being  dependent  on  the  draft, 
the  Committee  of  the  Society  recommended  that  a  boiler  rated  at 
any  horse-power  should  develop  that  power  when  using  the  best  coal 
ordinarily  sold  in  the  market  where  the  boiler  is  located,  fired  by  an 
ordinary  fireman  without  forcing  the  fires,  while  exhibiting  good 
economy;  and,  further,  that  the  boiler  should  develop  at  least  one- 
third  more  than  its  rated  power  when  using  the  same  fuel  and 
operated  by  the  same  fireman,  the  full  draft  being  employed  and  the 
fires  being  crowded ;  the  available  draft  at  the  damper,  unless  other- 
wise understood,  being  not  less  than  |  inch  water  column. 

Heating  Surface.  Boiler-makers  generally  measure  up  the  heat- 
ing surface  on  the  outside  of  all  tubes  and  flues,  as  the  result  is 


BOILERS  AND   STEAM-GENERATORS  65 

greater  than  when  the  inside  areas  are  considered.  It  is  a  mooted 
question  which  is  the  better  method  to  pursue.  Many  argue  that 
the  side  next  to  the  fire  should  be  considered,  because  it  is  technically 
the  correct  heating  surface.  Such  a  system  would  result  in  outside 
area  for  water-tubular,  and  inside  for  fire-tubular  boilers.  Others 
say  that  the  outside  should  be  considered  in  all  cases,  because  (1)  it 
is  simpler,  since  the  diameters  of  all  boiler-tubes  are  catalogued  and 
ordered  on  outside  measurement;  (2)  there  is  no  need  of  being  so 
very  accurate,  since  the  heat-transmitting  power  is  not  constant, 
but  varies  with  position  and  thickness;  and  (3)  more  is  gained  for 
comparison  by  adopting  a  uniform  method  for  all  cases.  Neither 
method  covers  every  form.  For  instance,  what  should  be  considered 
the  heating  surface  of  such  special  shapes  as  the  Serve  tube  (Fig.  55)  ? 
Its  heating  surface  is  certainly  greater  than  the  outside  area,  but 
is  not  effectively  equal  to  the  inside  area  when  the  surface  of  the 
ribs  is  included.  It  may  be  asked  what  is  its  heat-transmitting 
surface  when  partly  filled  with  soot  between  the  lower  ribs? 

The  American  Society  of  Mechanical  Engineers  favors  a  com- 
putation of  area  of  surface  of  shells,  tubes,  furnaces  and  fire-boxes 
in  contact  with  the  fire  or  hot  gases.  The  outside  diameter  of  water- 
tubes  and  the  inside  diameter  of  fire-tubes  are  to  be  used  in  the 
computation.  It  is  best  to  compute  the  total  area  as  accurately  as 
possible,  and  state  separately  the  square  feet  of  effective  water- 
heating  surface  and  of  steam  or  superheating  surface.  All  surfaces 
below  the  water-line  having  fire  or  hot  gases  on  one  side  and  water 
on  the  other  are  water-heating  surfaces ;  and  all  above  the  water-line 
having  hot  gases  on  one  side  and  steam  on  the  other  are  superheat- 
ing surfaces.  Any  surface  below  the  line  of  the  grate  to  which  the 
flames  do  not  have  access  should  not  be  considered,  nor  any  surface 
that  may  be  covered  by  brickwork  or  bridge  walls.  Only  three- 
quarters  of  the  bottom  of  horizontal-shell  boilers  set  in  brickwork 
tangent  to  the  shell,  should  be  taken,  as  the  part  on  each  side  next 
to  the  brick  walls  is  not  effective.  If  the  brick  walls  are  corbeled 
off  from  the  shell,  then  the  full  area  may  be  taken.  For  corrugated 
and  Morison  suspension  furnaces,  use  the  area  due  to  the  mean 
diameter  and  add  14£  and  9T\  per  cent  for  additional  surface 
respectively.  For  the  Purves  ribbed  furnace  use  the  outside 
diameter  of  flat  part  and  add  11  per  cent. 

Since  the  tube-sheets    are  not  very  effective,  many  engineers 


66  STEAM-BOILERS 

neglect  them  altogether  and  figure  the  tube  surface  on  the  extreme 
length  of  tube.  While  the  result  between  this  method  and  that  of 
computing  the  area  of  tube-sheets  between  tubes  plus  the  area  of 
tubes  figured  on  their  length  between  tube-sheets  is  nearly  the  same, 
the  author  favors  the  latter  method  as  being  the  more  uniform  and 
accurate  for  all  cases.  When  the  feed-water  is  heated  by  the 
products  of  combustion,  such  area  of  surface  should  be  stated, 
but  not  included  as  water-heating  surface. 

When  the  heating  surface  consists  nearly  all  of  tube  surface,  the 
efficiency  of  the  tubes  as  measured  by  the  total  evaporation  will  be 
found  to  vary  with  their  length,  and  nearly  in  the  following  ratio : 

Length  of  tubes,  in  diameters.  .      60  50  40  30  20 

Relative  water  evaporation. ...    1.00       0.91       0.83       0.75       0.67 

If  the  length  exceeds  60  diameters,  the  evaporating  efficiency 
of  the  increased  heating  surface  falls  rapidly.  It  is  advisable,  there- 
fore, not  to  make  the  tubes  over  50  or  60  diameters  in  length,  and 
to  use  more  tubes  or  tubes  of  a  different  size  in  order  to  make  up 
any  deficiency  in  surface. 

The  text-books  usually  state  the  ratio  of  heating  surface 
divided  by  grate  surface  for  various  boilers  to  be : 

For  plain  cylindrical from  10  to   15 

"   Cornish "  20  "    25 

"   Lancashire "  20  "    30 

"   Cylindrical  tubular "  95  •'    40 

"   Marine,  natural  draft "  28  "    35 

"      forced  draft "  35  "    50 

"   Water-tubular "  30  "    40 

"   Locomotive,  with  blast "  50  "  130 

These  figures  can  be  taken  as  representing  average  results,  but 
it  is  evident  that  for  any  particular  case  the  ratio  must  depend  on 
the  kind  of  fuel  and  on  the  rate  of  combustion.  The  dominating 
idea  is  to  absorb  all  the  heat  possible,  leaving  only  sufficient  for  pur- 
poses of  draft. 

The  quantity  of  water  that  will  be  evaporated  from  each  square 
foot  of  heating  surface  is  a  very  variable  quantity,  and  can  only  be 
foretold,  even  approximately,  by  those  having  had  considerable 
experience.  As  a  guide,  however,  it  may  be  stated  that  each  square 


BOILERS  AND  STEAM-GENERATORS  67 

foot  of  heating  surface  may  be  expected  to  evaporate  per  hour,  under 
conditions  usually  obtained  in  practice : 

In  stationary  boilers,  moderate  draft from  2  to  3    pounds 

"         "              "         fairly  strong  draft "  3  "  4  " 

strong  draft "  4  "  5J       " 

"         "              "          very  strong  draft "  5J  "  8  " 

"  marine  boilers,  moderate  draft "  3  "5  " 

strong  draft "  5  "7 

"         "         "         very  strong  draft "  7  "  8  " 

Such  results  are  obtained  by  dividing  the  total  evaporation  by 
the  water-heating  surface.  All  the  heating  surface  is  not,  however, 
equally  effective,  but  some  portions  evaporate  many  times  the 
quantity  of  others.  Surfaces  which  are  horizontal  or  nearly  so, 
and  those  so  placed  that  the  gases  will  not  pass  along  them  in 
"stream"  lines,  but  rather  impinge  against  them,  are  considered 
the  best.  Also,  those  parts  which  are  exposed  to  a  convection 
current  washing  away  bubbles  of  steam  as  fast  as  formed,  arc 
better  than  those  against  which  the  water  is  more  nearly  quiescent. 

The  water-heating  surface  varies  in  efficiency  according  to 
character  and  location.  Shell  heating  surface  is  more  efficient  than 
the  ordinary  tube  heating  surface.  Thus  9  square  feet  of  plain 
cylindrical  boiler  surface  is  about  equivalent  to  a  B.H.P.,  while  12 
to  15  square  feet  are  required  in  horizontal  return-tubular  boilers. 
The  former  type  of  boiler,  however,  fails  in  comparison  on  a  basis 
of  economy  in  steam  production. 

George  H.  Barrus  states  in  " Boiler  Tests"  that  little  or  nothing 
is  gained  in  evaporation  with  anthracite  coal  when  the  ratio  of 
heating  to  grate  surface  is  greater  than  36  to  1,  and  considers  that 
about  the  best  ratio  for  horizontal  tubular  boilers.  The  result  was 
based  on  average  results  from  a  number  of  tests,  all  having  low 
temperatures  for  the  escaping  gases  and  rates  of  combustion  ex- 
ceeding 9  pounds  with  natural  draft,  but  not  exceeding  12  pounds. 
When  the  ratio  was  increased  to  65  to  1  there  was  an  actual  loss. 
With  bituminous  coal  in  horizontal  tubular  boilers  he  found  better 
economy  with  greater  ratios;  thus  at  42  to  1  the  gases  still  retained 
high  temperatures,  and  the  best  result  in  his  tests  was  at  a  ratio  of 
53  to  1.  He  also  found  that  in  the  same  boiler  the  temperature  of 
escaping  gases  was  always  higher  with  bituminous  than  with  anthra- 


68  STEAM-BOILERS 

cite  coal,  showing  that  more  heating  surface  is  needed  for  the 
former.  Therefore  for  bituminous  coal  the  ratio  should  be  between 
45  and  50  to  1,  when  rate  of  combustion  is  about  10  to  12  pounds 
of  coal  per  square  foot  of  grate  per  hour.  He  further  states  that 
these  proportions  gave  good  results  in  vertical  boilers ;  and  sees  no 
reason  to  change  them  for  the  sectional  or  water-tubular  class. 

From  a  careful  study  of  the  subject  it  appears  that  there  is  no 
economy  in  forcing  boilers  beyond  their  proper  capacity,  as  then  the 
loss  of  heat  up  the  stack  becomes  excessive  from  lack  of  heating 
surfaces  in  relation  to  the  coal  burned.  In  general,  boilers  are  too 
often  operated  with  a  deficiency  of  heating  surface.  The  amount 
of  this  heating  surface  should  increase  with  the  rate  of  combustion, 
starting  with  the  values  mentioned  by  Barrus.  In  the  author's 
practice  the  question  arose  how  to  diminish  the  fuel  account  in  a 
certain  plant.  No  test  or  data  could  be  obtained  beyond  simple 
inspection  with  the  eye.  It  was  recommended  to  add  50  per  cent 
to  the  battery  of  boilers,  everything  else  being  retained  as  it  existed. 
The  change  caused  a  remarkable  saving,  due  to  a  better  ratio  of 
heating  to  grate  surface  and  a  consequent  reduction  in  loss  due  to 
high  temperatures  of  escaping  gases,  as  well  as  to  a  saving  of  coal 
raked  through  the  grate-bars  by  the  continual  forcing  of  fires. 

The  Design.  While  the  design  of  a  boiler  is  not  a  difficult 
problem,  it  is  necessary 'in  order  to  attain  success  to  keep  in  mind 
the  fundamental  principles  involved.  The  engineer  should  have 
some  practical  knowledge  of  the  boiler-maker's  methods  of  handling 
the  pieces,  or  the  finished  boiler  will  differ  from  the  drawing  in  many 
details.  This  knowledge  can  only  be  obtained  by  practice,  and  it 
is  this  extended  experience  which  should  enable  the  engineer  to  pro- 
duce a  better  design  than  the  manufacturer,  since  he  has  become 
familiar  with  the  methods  of  many  boiler-shops  and  is  thus  enabled 
to  select  the  best  details,  while  the  boiler-maker  is  apt  to  favor  the 
methods  of  his  own  practice  to  which  usage  has  made  him  accus- 
tomed. 

The  engineer  should  have  clearly  in  mind  just  what  results  he 
wishes  to  obtain  before  he  commences  his  plans.  The  points  to  be 
determined  may  be  stated  thus : 

First.  The  rate  of  combustion  desirable  or  practicable.  This 
rate  depends  upon  the  draft. 

Second.  The  type  of  boiler.     This  will  depend  largely  on  the 


BOILERS  AND  STEAM-GENERATORS  69 

quality  of  feed-water,  liability  for  overwork,  cost  of  manufacture, 
erection,  operation  and  maintenance. 

Third.  The  quantity  of  steam  demanded.  Upon  this  will  depend 
the  amount  of  power  to  be  put  into  one  boiler,  and  therefore  the 
actual  number  required. 

Fourth.  The  kind  of  fuel  and  the  quantity,  as  well  as  the 
efficiency  that  may  be  expected. 

Fifth.  The  ratio  of  heating  to  grate  surface  and  the  actual  areas 
required  to  burn  the  fuel  and  absorb  the  heat. 

Sixth.  The  nature  of  the  setting  and  the  manner  of  making 
the  steam  and  wrater  connections. 

Seventh.  The  necessary  drawings,  showing  arrangements  of  all 
details  and  connections.  These  drawings  are  usually  made  to  a 
scale  of  one  inch  to  one  foot,  with  details  to  larger  scale  as  may  be 
convenient. 

In  making  the  design,  care  must  be  taken  to  give  the  maker 
ample  room  for  laps,  flanging,  etc.,  otherwise  the  dimensions  will 
not  be  as  expected.  This  is  a  very  common  fault  with  good  design- 
ers, and  is  especially  liable  to  occur  when  only  outline  plans  are 
made.  Since  most  boiler-makers  lay  out  the  work  to  full  scale  com- 
mencing at  the  bottom,  all  errors  are  cumulative,  with  the  result  of 
raised  water-line  and  diminished  steam-room.  The  latter  is  seldom 
made  too  large,  so  that  the  fault  is  serious  and  liable  to  produce 
foaming. 

The  scantlings  will  be  treated  in  another  chapter.  The  principles 
involved  are  simple,  and  although  attempts  are  made  to  obtain 
improved  results  by  changes  in  details  and  in  general  arrangement, 
little  if  any  gain  is  produced  by  complication.  The  best  boilers  of 
the  various  well-known  types,  although  of  diverse  forms,  are  prac- 
tically equal  when  tested  under  conditions  suited  to  the  designs, 
the  results  published  in  trade  catalogues  notwithstanding. 

In  preparing  the  design,  it  is  well  to  keep  in  mind  the  following 
suggestions,  remembering  that  any  plan  must  be  one  of  "give  and 
take."  Therefore  weigh  the  advantages  against  the  disadvantages, 
and  settle  each  question  as  it  occurs. 

First.  Have  as  few  joints  and  double  thicknesses  of  metal 
exposed  to  the  fire  as  possible. 

Second.  Protect  furnace,  flues  and  tubes  from  sudden  impinge- 
ment of  cold  air. 


70  STEAM-BOILERS 

Third.  Provide  against  delivery  of  cold  feed-water  upon  hot 
plates  or  tubes. 

Fourth.  Provide  for  a  good  circulation  in  order  to  carry  away 
steam  from  the  heating  surfaces  as  soon  as  formed. 

Fifth.  Provide  ample  passages  for  upward  as  well  as  for  down- 
ward currents,  and  arrange  that  they  shall  not  interfere. 

Sixth.  If  of  sectional  type,  provide  ample  passages  between  the 
various  sections,  so  as  to  equalize  pressure  and  water-level  in  all. 

Seventh.  Provide  sufficient  water  surface  to  allow  the  steam  to 
separate  quietly. 

Eighth.  Provide  ample  steam-room,  so  as  to  maintain  a  constant 
water-level  and  to  prevent  foaming. 

Ninth.  Provide  for  carrying  the  hot  gases  to  all  parts  of  the 
heating  surfaces  and  prevent  them  from  making  a  short  circuit  to 
the  chimney,  or  while  still  at  high  temperature  from  reaching  tubes 
containing  steam  only,  unless  such  surfaces  are  arranged  for  super- 
heating. 

Tenth.  To  so  arrange  the  parts  that  they  may  be  constructed 
without  mechanical  difficulty  or  excessive  expense. 

Eleventh.  To  select  a  form  that  will  not  unduly  suffer  under 
the  action  of  the  hot  gases. 

Twelfth.  To  make  all  parts  accessible  for  cleaning  and  repair. 

Thirteenth.  To  give  each  part,  as  nearly  as  possible,  equal 
strength.  Such  parts  as  are  most  liable  to  loss  from  corrosion,  etc., 
should  be  made  the  strongest,  so  that  the  boiler  when  old  shall  not 
be  rendered  useless  by  local  defects. 

Fourteenth.  To  adopt  a  reasonably  high  factor  of  safety  in  pro- 
portioning the  parts. 

Fifteenth.  To  endeavor  to  secure  careful,  intelligent  and  effi- 
cient management. 

The  different  types  and  arrangement  of  steam-boilers  are  so 
numerous  as  to  be  impossible  to  describe  all.  A  few  of  the  more 
general  types  will  be  selected  as  illustrations. 

The  Plain  Cylindrical  Boiler  consists  of  a  long  cylindrical  shell 
built  up  with  plates  (Fig.  9).  The  heads  are  nearly  always  bumped, 
so  that  the  boiler  is  self-sustaining  and  requires  no  stays. 

The  shell  is  set  in  brickwork,  and  is  supported  by  rods  from 
above.  The  eye  in  the  rod  end  engages  a  hook  riveted  to  shell,  or 
the  rod  end  may  have  a  hook  formed  on  it  and  catch  a  ring  riveted 


BOILERS  AND  STEAM-GENERATORS 


71 


to  the  top  of  shell.  The  rods  can  be  made  with  turnbuckles  or  with 
a  thread  and  nut  on  upper  end  so  as  to  adjust  the  length. 

The  boilers  should  be  slightly  inclined  to  facilitate  draining, 
one  inch  or  two  inches  in  the  total  length  being  generally  sufficient. 

The  grate  is  usually  made  common  to  two  or  three  boilers,  a 
feature  which  permits  the  use  of  cheap  grades  of  fuel.  The 
objection  is  the  necessity  of  laying  off  the  other  boilers  in  order  to 
repair  or  clean  one.  The  space  between  the  boilers  is  closed  by 
means  of  arched  fire-brick  resting  on  the  shells 


FIG.  9.— End  of  a  Plain  Cylindrical  Boiler. 

These  boilers  seldom  exceed  42  inches  in  diameter  by  50  feet  in 
length.  A  common  size  is  36  inches  in  diameter  by  30  feet  long. 

They  are  cheap,  easily  handled  and  quickly  cleaned.  As  there 
is  difficulty  in  obtaining  heating  surface,  and  as  they  are  not 
economical  except  in  first  cost,  this  type  is  little  used  unless  in  con- 
nection with  the  waste  gases  obtained  from  certain  metallurgical 
works.  They  require  large  floor-space,  which  is  often  an  objection- 
able feature. 

The  Horizontal  Return-tubular  Boiler  is  a  form  in  extensive 
use  in  American  practice  (Figs.  10,  11,  and  12).  It  is  simple,  inex- 
pensive, and,  when  properly  handled,  is  durable.  It  contains  con- 
siderable heating  surface  for  the  space  required,  and  is  economical. 

The  shell  varies  in  thickness  from  -J-  inch  upwards,  according  to 
pressure.  The  heads  are  usually  made  f  inch  thick  for  boilers  less 
than  36  inches  diameter;  T7^-  inch,  from  36  inches  to  60  inches;  J 
inch,  from  60  inches  to  72  inches;  and  T9¥  inch  for  all  over  72  inches. 

The  fire  is  on  an  external  grate,  and  the  products  pass  beneath 


72 


STEAM-BOILERS 


BOILERS  AND  STEAM-GENERATORS 


73 


the  shell  to  the  back  end,  and  return  through  tubes  to  the  front, 
where  they  pass  into  the  smoke-connection.  Occasionally  the 
products  are  again  made  to  pass  along  the  top  of  the  shell  to  the  rear 
end,  but  this  practice  is  rare,  as  it  makes  an  inconvenient  arrange- 
ment for  reaching  the  steam  and  other  attachments  on  top  of  the 
shell. 

These  boilers  are  made  with  either  an  extended  (Fig.  10)  or  flush 


FIG.  10a. — Horizontal  Return-tubular  Boiler. 
Front  and  section  of  Fig.  10. 

front  (Figs.  11  and  12).  The  former  is  the  cheaper,  and  is  made  by 
extending  the  shell  plating  about  15  inches  beyond  the  front  head, 
so  as  to  form  a  smoke-box,  to  the  top  of  which  the  smoke-flue  is 
connected  by  an  angle  or  cast-iron  ring.  The  front  is  closed  by  a 
hinged  door,  made  high  enough  to  expose  all  the  tubes  for  cleaning. 
With  the  flush  front,  the  head  end  of  the  boiler  can  be  the 


STEAM-BOILERS 


BOILERS  AND  STEAM-GENERATORS 


75 


same  as  the  back  end,  with  the  smoke-box  constructed  in  the  brick 
setting. 

The  fronts  in  either  case  are  generally  made  of  cast  iron,  with 
panel- work  more  or  less  elaborate.  The  half -front  fits  around  the 
extension  smoke-box,  while  the  flush  front  extends  to  the  top  of  the 


FIG.  lla. — Horizontal  Return -tubular  Boiler. 
Front  and  section  of  Fig.  11. 

brick  setting.     The  flush  front  has  a  door,  usually  made  in  halves 
with  hinges  on  the  sides,  to  expose  the  tube-ends. 

The  settings  are  made  of  brick.  The  shell  frequently  rests  on 
the  side  walls,  being  supported  by  cast-iron  lugs,  cast  to  fit  the  shell. 
There  are  two  lugs  on  each  side,  although  some  very  large  boilers 
have  three.*  The  lugs  are  generally  one  inch  thick,  with  a  stiffening 

*  For  boilers  66  inches  in  diameter  and  larger,  it  is  best  to  use  four  lugs 
on  a  side,  placing  them  in  pairs  close  together. 


76 


STEAM-BOILERS 


1 


BOILERS  AND   STEAM-GENERATORS 


77 


web  }  to  1  inch  thick.  These  lugs  are  bolted  to  the  shell,  although 
small  lugs  are  sometimes  riveted  on.  A  bolt  screwed  through  the 
shell  and  lug,  fitted  with  a  nut,  makes  a  good  arrangement.  The 
bottom  flange  is  from  8  to  14  inches  long  by  6  to  12  inches  wide. 

The  lug  rests 
on  a  cast-iron 
or  steel  plate 
built  in  the 
brickwork. 
Cast  iron  is 
the  better  The 
plate  should 
have  a  surface 
of  at  least  one 
square  foot. 
When  of  steel 
it  should  be  f 
inch  thick,  and 
when  of  cast 
iron  J  or  1  inch 
thick.  The 
front  lugs  rest 
directly  on  the 
plates,  but  the 
back  lugs 
should  have 
rollers  not  less 
than  one  inch 


FIG.  12a. — Horizontal  Return-tubular  Boiler. 
Section  of  Fig.  12. 


in  diameter,  between  lug  and  plate,  to  let  the  boiler  accommodate 
itself  by  expansion  and  contraction. 

This  method  is  open  to  many  objections.  It  is  difficult  to  build 
up  the  brick  walls  under  the  boiler  to  just  the  proper  height  for  the 
several  lugs.  If  one  is  too  high  or  too  low,  it  will  cause  a  twisting 
strain  on  the  shell.  Furthermore,  it  is  almost  impossible  to  get  the 
rollers  to  bear  true  and  even.  One  is  apt  to  carry  the  weight  and 
the  others  be  loose.  Also,  the  projecting  rivet-heads  are  liable  to 
injure  the  brick  setting  as  the  boiler  expands  or  contracts. 

These  defects  in  setting  can  be  avoided  by  hanging  the  boiler  on 
suspension  links.  A  method  advocated  by  Mr.  O.  C.  Woolson 


78  STEAM-BOILERS 

(Trans.  Am.  Soc.  Mechanical  Engineers,  Vol.  XIX,  1898)  consists  in 
carrying  the  front  brackets  on  the  side  walls  and  suspending  the 
rear  end  from  a  link  supported  by  channels  placed  across  the  top  of 
the  setting  (Fig.  12) .  The  front  brackets  are  long  enough  to  put  the 
weight  on  the  outside  wall,  so  that  the  inside  fire-brick  lining 
can  be  taken  down  at  any  time  for  renewal.  The  buck-staves 
or  binder-bars  at  the  front  are  fastened  to  the  supporting  brackets, 
so  that  they  move  as  the  boiler  expands  and  relieve  the  brickwork. 
The  side  channels  at  the  rear,  which  carry  the  cross-channel,  form 
the  buck-staves  for  that  end. '  This  method  is  really  a  three-point 
suspension.  The  rivet-heads  are  kept  away  from  the  brick  walls 
by  using  a  3-inch  Z  bar  riveted  to  shell,  against  the  smooth  side  of 
which  the  side  walls  are  built. 

These  boilers  should  be  set  slightly  inclined  toward  the  end 
having  the  bottom  blow-off,  so  as  to  drain  freely.  About  one  inch 
is  sufficient. 

The  distance  between  the  back  head  and  the  rear  wall  should  be 
about  16  inches  for  boilers  less  than  58  inches  diameter,  and  from  18 
to  24  inches  for  larger  ones. 

The  distance  from  top  of  grate  to  under  side  of  shell  should  be 
as  great  as  possible  so  as  not  to  chill  the  gases.  It  is  often  made  too 
small.  Soft  coals  require  a  greater  height  than  hard  coals.  The 
distance  is  usually  26  to  30  inches  for  grates  4  feet  in  length,  and 
should  be  increased  in  proportion  to  length.  For  soft  coals  this 
distance  should  be  increased  by  about  20  per  cent. 

The  combustion-chamber  behind  the  bridge  wall  may  be  filled 
up  with  earth  or  ashes,  so  as  to  keep  the  hot  gases  near  the  shell, 
but  its  actual  shape  appears  to  make  little  difference.  It  is  well, 
however,  to  pave  the  floor  of  the  combustion-chamber,  that  the  heat 
may  be  radiated  back  as  much  as  possible.  A  clean-out  door,  large 
enough  for  a  man  to  pass,  will  be  found  convenient  at  the  rear  end 
of  the  combustion-chamber.  This  door  should  be  carefully  made 
and  set,  so  as  to  be  air-tight. 

The  side  and  rear  walls  are  best  made  double,  with  an  air-space 
between  them  about  2  or  4  inches  wide.  With  a  2-inch  space 
the  total  width  of  wall  would  be  18^  inches.  About  every  two  feet 
headers  should  be  run  from  wall  to  wall,  but  the  walls  should  not  be 
bonded  together.  The  air-space  prevents  radiation  of  heat,  as  well 
as  allowing  the  inside  wall  to  expand  freely. 


BOILERS  AND  STEAM-GENERATORS  79 

The  covering  of  the  back  connection  may  be  flat  or  arched. 
It  is  generally  carried  on  cast-iron  supports  of  tee  section.  If 
arch-bricks  are  used,  those  next  to  the  boiler-head  can  rest  on 
a  two-inch  angle  riveted  to  back  head  of  boiler.  The  lower  edge 
of  this  covering  should  be  below  the  water-line. 

The  blow-off  should  be  in  the  bottom  of  shell  near  the  rear 
end.  The  pipe,  if  unprotected,  is  liable  to  burn  off,  as  there  is 
no  circulation  through  it.  It  can  be  protected  by  covering  with 
pieces  of  cast  iron  or  hard-burned  tile  pipe,  slipped  over,  as  shown 
in  Fig.  12.  By  connecting  this  blow-off  pipe  with  a  branch  enter- 
ing the  boiler  near  the  water-line  a  circulation  can  be  main- 
tained which  will  materially  assist  in  preventing  injury,  but  such 
a  connection  adds  extra  joints  and  parts  that  may  give  trouble. 
When  properly  made,  this  circulating  connection  can  be  com- 
mended. 

The  tubes  are  often  too  close  to  the  shell.  They  should  be 
spaced  from  the  sides  of  shell  far  enough  to  allow  a  generous  down- 
current  water-space.  The  distance  from  side  of  shell  to  out- 
side of  nearest  tube  should  not  be  less  than  4  inches,  and  a 
vertical  line  drawn  from  the  point  where  water-line  strikes  the 
side  of  shell  should  pass  outside  the  top  row  of  tubes.  The 
tubes  should  be  in  horizontal  and  vertical  rows,  and  not  be 
staggered. 

There  should  be  a  manhole  in  shell  above  the  tubes,  and  when 
possible  one  in  front  head  below  the  tubes. 

Figs.  10,  11  and  12  show  different  designs.  The  good 
points  of  one  may  be  embodied  in  another  to  suit  require- 
ments. 

The  Upright  or  Vertical  Boiler  is  a  very  useful  form  where 
economy  of  floor-space  is  a  requisite.  The  small  sizes  are  easily 
portable,  and  no  setting  is  required  (Figs.  13  and  14). 

When  the  size  will  permit,  they  should  be  made  of  one  sheet, 
thus  having  one  vertical  seam,  which  should  be  i  double-riveted, 
and  two  ring-seams  at  the  ends,  which  may  be  single-riveted. 
When  more  than  one  sheet  must  be  used,  the  lap  on  the  ring- 
seam  should  be  downward  on  the  inside,  so  as  not  to  obstruct 
the  downward  current  of  water  or  form  a  ledge  to  catch  sedi- 
ment. 


80 


STEAM-BOILERS 


TABLE  XI 

HORIZONTAL   RETURN-TUBULAR    BOILERS 
A  List  of  Commercial  Sizes* 


Horse-power  

30 

35 

40 

45 

50 

60 

70 

75 

Heating    surface,   in 
square  feet 

429 
42 
13' 

I 

38 

506 
44 
13' 

f; 

46 

568 
48 
13'  1" 

I 

52 

618 
50 
14'  2" 

A 

I 

52 
42 
37 
4 
4 
24 

684 
54 
14'  2" 

A 

13 
58 
50 
40 
4 

4* 

26 

800 
54 

16'  2" 

tV 

15 
58 
50 
40 
4 
5 
26 

944 
60 
15'  4" 

TV 

14 
76 
60 
50 
5 
5 
28 

1010 
60 

16'  4" 

1 

TV 

15 

76 
60 
50 
5 
5 
28 

Diameter   of    boiler, 
in  inches  
Length  of  boiler,  in 
feet  and  inches  .  .  . 
Thickness  of  shell  .  .  . 
Thickness  of  head.  .  . 
Length  of  tubes,  feet 
No.   of  tubes  3"  in 
diameter  
No.  of  tubes  3£"  in 
diameter 

No.   of  tubes  4"   in 
diameter  

4 
4 
24 

Diameter  of  nozzles, 
in  inches         

3 
4 
20 

3 
4 
22 

Length  of  furnace,  in 
feet             

Diameter  of  stack  re- 
quired, in  inches  .  . 

Wt.   of    bare  boiler, 
about 

5,OOC 

5,500 

6,400 

6,800 

7,300 

8,550 

10,000 

10,500 

Horse-power 

80 

90 

100 

125 

150 

175 

200 

Heating  surface,  sq.  ft  ... 
Diameter  of  boiler,  inches 
Length  of  boiler,  in  feet 
and  inches  
Thickness  of  shell     

1080 
60 

17'  4" 

TV 
16 
76 
60 
50 
5 
5 

28 

1249 
66 

16'  5" 

1 

15 
96 
72 
60 
6 
5* 

32 

1350 
66 

17'  5" 

1 

96 

72 
60 
6 
5* 

32 

1674 

72 

17'  6" 

I 

122 
96 

74 
6 
6 

36 

1829 

72 

19'  6" 

iV 

18 

96 
74 
6 
6'6i" 

38 

2115 

78 

19'  6" 

t 

18 

112 
90 

7 
6'  6}" 

40 

2511 
84 

19'  8" 

A 

18 

136 

108 

8 

7 

42 

Thickness  of  head  
Length  of  tubes,  in  feet.  .  . 
No.  of  tubes  3"  in  diam.  .  . 
No.  of  tubes  3£"  in  diam  . 
No.  of  tubes  4"  in  diam.  .  . 
Diameter  of  nozzles,  in  ins. 
Length  of  furnace,  in  feet  . 
Diameter    of     stack    re- 
quired in  inches      .    .  . 

Weight    of    bare    boiler, 
about      

11,200 

13,300 

14,000 

17,500 

18,500 

21,000 

25,000 

*  From  Catalogue  of  the  Bigelow  Co.,  New  Haven,  Conn. 


BOILERS  AND   STEAM-GENERATORS 


81 


The  upper  head  is  flanged  to  meet  the  shell.  At  the  bottom 
the  shell  and  fire-box  are  united  through  a  mud-ring  of  forged  iron 
or  steel,  or  the  fire-box  is 
flanged  below  the  grate  to 
meet  the  shell. 

The  fire-box  is  internal 
and  the  crown-sheet  forms 
the  lower  tube-sheet.  The 
tubes  support  and  stay 
the  crown-sheet  and  upper 
head. 

The  fire-box  sides  are 
stayed  to  the  shell  by 
bolts  screwed  through  both 
sheets  and  riveted  over. 
Sometimes  these  stay-bolts 
are  protected  by  sockets, 
made  of  pieces  of  pipe  cut 
just  the  length  between 
boiler-shell  and  fire-box. 

The  fire-box  sheet 
should  be  made  as  thin  as 
the  spacing  of  the  bolts 
will  permit,  so  as  to  pre- 
vent burning  and  to  trans- 
mit the  heat  freely.  The 
mud-ring  should  be  deep 
enough  to  overcome  the 


tendency  to  turn;  due  to 
the  greater  expansion  of 
the  tubes  and  fire-box  over 
that  of  the  shell. 

The  width  of  the  water- 
leg  should  be   as   wide   as 


FIG.  13. — Upright  or  Vertical  Boiler. 


convenient  in  order  to  reduce  the  bending  of  the  stay-bolts  as 
much  as  possible,  due  to  the  greater  expansion  of  the  fire-box 
sheet.  The  width  should  never  be  less  than  2£  inches  in  the 
smallest  boilers,  and  2f  or  3  inches  is  preferable. 

The  tubes  are  generally  two  inches  in  diameter   but  may  be 


82 


STEAM-BOILERS 


increased  with  the  size  of  the  boiler.     In  the  ordinary  form  the 

upper  ends  of  the  tubes  are  in  the  steam-space  and  subjected  to 

extreme  heat,  which  may 
cause  injury.  In  conse- 
quence the  tubes  are 
sometimes  made  totally 
submerged  by  having  the 
upper  tube-sheet  below 
the  water-line,  and  con- 
necting it  with  a  smoke- 
flue  to  the  upper  head,  as 
in  Fig.  14. 

There  should  be  hand- 
holes  in  the  water-leg  just 
above  the  mud-ring  for 
cleaning  out  sediment. 
It  is  convenient  to  place 
a  chain  at  the  bottom  of 
the  water-leg  which  can 
be  worked  around  through 
the  hand-holes  to  assist  in 
removing  scale  and  dirt. 
There  should  be  another 
hand-hole  at  the  level  of 
the  crown-sheet,  so  placed 
as  to  reach  all  parts  for 
cleaning  and  inspection. 

The  height  of  the  fire- 
box should  be  as  great  as 
possible,  but  not  less  than 
20  inches  from  top  of 
grate  in  boilers  24  inches 
diameter,  and  36  inches 

in  boilers  60  inches  diameter. 

The  boiler  usually  rests  on  a  cast-iron  base,  which  forms  the 

ash-pit. 

The  Manning  Boiler  is  one  of  the  best-known  types  of  large 

size  vertical  tubular  boilers  (Figs.  15  and  15a). 

These  boilers  are  set  on  a  brick  foundation,  forming  the  ash-pit, 


FIG.  14. — Upright  or  Vertical  Boiler 
with  submerged  tube-sheet. 


TABLE  XII 

VERTICAL    TUBULAR    BOILERS 
A  List,  of  Commercial  Sizes 


Horse-power         

3 

5 

6 

7 

8 

10 

12 

15 

Heating-surface,  in  sq.  ft.  .  . 
Diameter  of  boiler,  inches.  . 
Height  of  boiler,  feet  
Diameter  of  furnace,  inches. 
Height  of  furnace,  inches.  .  . 
Thickness  of  shell  
Thickness  of  furnace  
Thickness  of  heads  
Number  of  2-inch  tubes.  .  .  . 
Length  of  tubes,  inches.  .  .  . 
Diameter  of  bottom  of  base, 
inches  
Height  of  base,  inches  
Height  of  bonnet,  inches.  .  . 
Height  of  boiler,  bottom  of 
base   to   top    of   bonnet, 
inches  . 

39 
21 
5 
16 
24 

* 

1 

20 
36 

27 
11 

8 

79 

91 

7 

58 
24 
5 
19 
24 

i 

31 

36 

31 
11 

9 

80 

92 

8 

72 
27 
5 
22 
24 

| 

39 
36 

35 
13 
10 

83 

95 
9 

84 
30 
5 
25 
24 
i 

46 
36 

37 
13 
11 

84 

96 
10 

100 
30 
6 
25 
24 
\ 

46 

48 

37 
13 
11 

96 

108 
10 

120 
32 
6 
27 
24 

1 
51 

48 

39 
13 
12 

97 

109 
11 

144 
34 

26* 
24^ 
i 

56 
54 

41 
13 
13 

104 

116 
12 

180 
36 

7 

24 
i 

64 
60 

43 
13 
13 

110 

122 
14 

Height  of  boiler,  bottom  of 
wheels    to    top    of    bon- 
net, inches. 

Diameter  of  smoke-stack  re- 
quired, inches.     .            .  . 

Weight    of    boiler    without 
fixtures  

750 
300 

900 
400 

1100 
425 

1300 
500 

1450 
500 

1540 
600 

1750 
650 

2100 
700 

Weight  of  fixtures  

Horse-power 

18 

20 

25 

30 

35 

40 

50 

Heating  surface,  in  square  feet.  .  . 
Diameter  of  boiler,  inches  
Height  of  boiler,  feet 

212 
40 
7* 
34* 
30 

238 
40 
7* 
34* 
30 

N& 

292 
44 

8 

30* 

A 

No.  2 

358 
48 
8 
42* 
30' 

412 

48 
8 
42* 
30' 

480 
48 
9 
42^ 
30 

578 
54 
9 
48* 
36" 

Diameter  of  furnace,  inches.    . 

Height  of  furnace,  inches  

Thickness  of  shell      

Thickness  of  furnace  

Thickness  of  heads  
Number  of  2-inch  tubes  
Length  of  tubes,  inches  
Diameter  of  bottom  of  base,  ins.  . 
Height  of  base,  inches  

74 
60 
47 
13 
13 

116 
128 
16 

84 
60 
47 
13 
13 

116 
128 
16 

95 
66 
50 
13 
16 

125 
137 
17 

t 

118 
66 
54 
13 
16 

125 
137 

IS 

138 
66 
54 
13 
16 

125 
137 

18 

138 

78 
54 
13 
16 

137 
149 
18 

| 

178 
72 
60 
13 
18 

139 
151 
22 

Height  of  bonnet,  inches.  .  

Height  of  boiler,  bottom  of  base  to 
top  of  bonnet  inches 

Height  of  boiler,  bottom  of  wheels 
to  top  of  bonnet,  inches 

Diam.   of   srnoke-stack  required, 
inches  . 

Weight  of  boiler  without  fixtures  . 
Weight  of  fixtures  

2600 
900 

2700 
900 

3500 
1000 

4000 
1050 

4250 
1050 

1850 
1050 

5550 
1200 

83 


84 


STEAM-BOILERS 


which  consists  of  a 
circular  wall  12£ 
inches  thick,  having 
the  inside  diameter 
the  same  as  that  of 
the  fire-box.  In 
order  to  provide  in- 
creased grate  area 
as  well  as  to  allow 
for  expansion,  the 
shell  is  enlarged 
by  a  double-flanged 
throat-piece  just 
above  the  top  of  the 
combustion-c  h  a  m  - 
ber . 

The  tubes  are 
generally  2J  inches 
diameter  and  from 
12  to  15  feet  long. 
They  are  arranged 
in  four  sections,  so 
as  to  leave  two 
cleaning-spaces,  like 
the  arms  of  a  cross. 
Opposite  these 
spaces  handholes  are 
located  to  reach  all 
parts  of  the  top  of 
the  crown-sheet. 

The  feed- water  is 
introduced  through 
a  perforated  pipe, 
located  near  the 
middle  of  the  boiler. 

The  Flue  and 
R  e  t  u  r  n-t  u  b  u  1  a  r 
Boiler  makes  a  very 
convenient  form  of 


FIG.  15. — Manning  Vertical  Boiler. 


BOILERS   AND   STEAM-GENERATORS 


85 


internally  fired  boiler  for  stationary  work  (Figs.  16,  16a  and  166). 
It  requires  no  setting  beyond  the  saddles,  which  may  be  either  of 
cast  iron  or  steel  built  up  with  angles  and  plates.  The  saddle  is 
curved  to  fit  the  shell  and  is  about  one-third  the  diameter  in  length. 
It  is  similar  to  the  Scotch  boiler,  but  has  an  external  back  con- 
nection for  draft  between  the  flue  and  tubes,  in  place  of  an  internal 
This  back  connection  is  lined  with  fire-brick.  There  may  be 


one. 


FIG.  15a. — Manning  Vertical  Boiler,    Sections  of  Fig.  15. 


one  or  two  furnace-flues  to  suit  the  diameter  of  shell.  The  length 
of  grate  should  not  exceed  twice  the  diameter  of  flue. 

These  boilers  are  economical,  suitable  for  mechanical  draft 
(especially  the  induced  draft),  and  are  entirely  self-contained. 

The  Cornish  Boiler  consists  of  a  cylindrical  shell  with  one  large 
flue  (Figs.  17  and  17a).  This  flue  has  a  diameter  of  about  one-half 
that  of  the  shell,  and  is  so  placed  as  to  leave  4J  or  5  inches  between  it 
and  the  nearest  part  of  the  shell.  On  the  continent  of  Europe  this 
flue  is  often  placed  on  one  side  with  the  object  of  increasing  the  cir- 
culation, but  no  material  advantage  is  noticed.  This  flue  is  built 
up  of  short  lengths  so  as  to  keep  its  thickness  as  thin  as  is  consistent 
with  strength.  It  is  frequently  strengthened  by  Galloway  tubes, 
as  shown  in  Figs.  17  and  45.  These  tubes  are  usually  about  10  or 
11  inches  in  diameter  at  the  top,  and  one-half  of  that  at  the 
bottom  end,  and  provide  additional  effective  heating  surface. 

The  boiler  is  fired  internally ;  the  gases  pass  through  the  flue  to 
the  back  end,  then  under  the  boiler  and  back  again  on  each  side, 


86 


STEAM-BOILERS 


BOILERS  AND  STEAM-GENERATORS 


87 


making  a  "split-return  draft."     At  other  times  the  gases  pass  to  the 
front  on  one  side  and  back  on  the  other,  making  a  "wheel  draft." 

The  boiler  is  set  in  brickwork.  The  back  head  is  usually 
flanged  in  to  meet  the  shell,  while  the  front  head  is  fastened  with  an 
angle  placed  on  the  outside  of  the  shell.  This  arrangement  allows 
a  certain  amount 
of  spring  in  the 
head  and  thus  pro- 
vides for  the  expan- 
sion of  the  flue. 

As  all  parts  are 
easily  cleaned,  this 
boiler  can  be  used 
with  hard  waters, 
although  the  large 
flue  and  lack  of 
heating  surface  are 
decided  drawbacks. 
I  n  consequence 
Cornish  boilers  are 
not  used  as  much  as 
formerly,  and  are 
not  as  favorably 
received  as  the 
Lancashire. 

The  Lancashire 
Boiler  is  similar  to 
the  Cornish,  but  has 
two  flues  instead  of 


one    (Figs.   18   and 

18a).       These  flues 

have  a  diameter  of 

about  one-third  that  of  the  shell,  and  are  placed  so  as  to  leave 

about  4  or  4^  inches  between  them  and  between  the  flues  and  shell. 

The  strengthening  rings -on  the  flues  can  be  spaced  so  as  to  stagger 

and  thus  leave  more  room  for  cleaning. 

Common  sizes  for  these  boilers  are  7  feet  6  inches  diameter  by 
30  feet  long,  with  flues  each  36  inches  diameter;  or  8  feet  diameter 
by  33  feet  long,  with  flues  each  39  inches  diameter.  The  usual 


FIG.  IBa. — Flue  and  Return-tubular  Boiler. 
Pront  view  and  section  of  Fig.  16. 


STEAM-BOILERS 


pressure  is  100  pounds  on  the  square  inch,  although  pressures  as 
high  as  125  pounds  are  not  uncommon.  When  the  flues  are  fitted 
with  Galloway  tubes  160  pounds  is  sometimes  used.  These  boilers 
are  occasionally  fitted  with  three  smaller  flues,  and  are  then  known 
as  "  three-flue  Lancashire  boilers."  When  the  furnace-flues  unite 

into  one  large  flue, 
strengthened  with 
Galloway  tubes, 
they  are  called  Gal- 
loway boilers  (Figs. 
19  and  20). 

The  setting  is  of 
brick.  The  shell 
may  be  supported 
on  cast-iron  sad- 
dles, as  in  Fig.  18; 
or  on  fire-clay  seat- 
ing blocks,  as  in 
Figs.  17  and  20. 
These  blocks  have 
a  bearing  surface 
about  5  inches  wide, 
and  extend  the  full 
length  of  the  boiler. 
The  shell  may  be 
carried  on  one  cast- 
iron  saddle,  as  in 


FIG.  166. — Flue  and  Return-tubular  Boiler. 
Back  view  of  Fig.  16. 


Fig.  19.  The  front  end  is  then  supported  on  the  brickwork,  while 
the  rear  end  is  carried  on  the  saddle  made  of  three  parts  to  allow 
play  for  expansion — a  foot-block,  a  saddle  to  fit  the  shell,  and  an 
intermediate  rocker.  There  is  also  a  brick  safety-wall,  which 
deflects  the  hot  gases  from  the  iron  support.  The  draft  may 
pass  like  that  of  the  Cornish  boiler  or  be  made  to  return  over  the 
top. 

Any  of  the  settings  illustrated  in  Figs.  17,  18,  19,  and  20  apply 
alike  to  Galloway,  Cornish  and  Lancashire  boilers,  and  any  form  of 
strengthening  for  the  flues  may  be  adopted. 

The  flues  are  sometimes  reduced  in  diameter  at  the  rear  end  to 
facilitate  removal  and  give  sufficient  clearance  from  shell  to  allow 


90 


STEAM-BOILERS 


the  back  head  to  spring,  which  head  must  be  fastened  to  the  shell 
by  an  internal  flange  or  angle.     The  former  method  is  much  the 

better  as  being 
stronger  and  less 
stiff.  An  outside 
angle,  like  that  on 
front  head,  cannot 
be  used,  as  it  would 
interfere  with  the 
draft- current  and 
rapidly  burn  away. 
The  Lancashire 
boiler  is  an  economi- 
cal type  and  is  well 
liked  in  Europe. 
Best  results  are  ob- 
tained when  used 
with  an  economizer 
or  feed-water  heater 
placed  in  the  flue 
leading  to  the 
chimney,  especially 


FIG.  17a. — Cornish  Boiler. 
Front  view  and  section  of  Fig.  17. 


if  high  rates  of  com- 
bustion are  adopted. 
It  requires  a  large 

floor-space,  and  has  been  but  little  used  in  America,  chiefly  on  that 
account. 

The  bottom  blow-off  connection  is  customarily  made  at  the 
front  end.  Great  care  should  be  taken  not  to  conceal  it  in  the 
brick  setting,  as  accidents  have  occurred  from  undiscovered  cor- 
rosion of  this  part. 

The  low-water  and  the  dead-weight  safety-valves  shown  in  the 
illustrations  are  not  necessarily  a  part  of  the  design,  but  are  com- 
monly adopted  in  foreign  practice. 

The  Scotch  or  Drum  Boiler  consists  of  a  cylindrical  shell, 
internally  fired  in  large  furnace-flues,  the  gases  returning  through 
a  back  connection,  or  combustion-chamber,  and  a  bank  of  tubes. 
It  may  be  single-ended  as  in  Figs.  21  and  22,  or  double-ended  as  in 
Fig.  23. 


91 


92 


STEAM-BOILERS 


It  is  principally  used  in  marine  work,  where  it  is  much  liked  on 
account  of  its  reliability,  but  can  be  adopted  for  stationary  practice. 

It  is  necessarily  heavy, 
due  to  the  thickness  of 
metal  and  large  amount 
of  water  contained;  and 
strong  efforts  have  been 
made,  coincident  with  the 
increase  of  steam-pres- 
sures, to  adopt  other 
forms.  It  is  entirely  self- 
contained;  is  supported 
on  saddles ;  is  very 
economical ;  and,  when 
properly  designed,  is  not 
difficult  to  clean  or  re- 
pair. 

There    may    be    one, 
that    number   if    double- 


FIG.  18a. — Lancashire  Boiler. 
Front  view  and  section  of  Fig.  18. 


two,  three  or  four  furnaces,  or  twice 
ended.  It  is  a  frequent  fault  to  use  furnaces  of  too  small  a 
diameter.  Two  large  furnaces  are  better  than  three  small  ones, 
or  three  large  ones  than  four  small.  Furnaces  less  than  33 
inches  in  diameter  cramp  the  area  over  bridge  wall  and  the 
height  of  ash-pit,  thus  restricting  the  draft  and  chilling  the  gases 
with  the  low  crown.  The  back  connection  or  combustion-chamber 
may  be  common  to  all  furnaces  or  be  divided,  one  to  each.  With 
four  furnaces  it  is  usual  to  fit  two  combustion-chambers,  each 
common  to  two  furnaces.  Separate  combustion-chambers  are  to 
be  preferred  with  mechanical  draft.  When  double-ended  there 
should  be  separate  combustion-chambers  for  each  end. 

The  tubes  should  be  arranged  in  nests,  leaving  a  clear  vertical 
space  between  the  banks  of  tubes  and  between  the  tubes  and  shell. 
These  spaces  should  be  about  twice  the  pitch  of  tubes.  The  distance 
from  the  side  of  shell  to  the  outside  of  nearest  tube  should  not  be 
less  than  8  inches,  and  a  vertical  line  from  the  point  where  the 
water-line  strikes  the  inside  of  the  shell  should  pass  outside  of  the 
two  top  rows  of  tubes,  otherwise  the  boiler  is  liable  to  prime.  The 
uppermost  row  of  tubes  should  be  at  least  0.3  of  the  boiler  diam- 
eter below  the  top  of  the  shell,  in  order  to  obtain  proper  water- 


BOILERS  AND  STEAM-GENERATORS 


93 


94 


STEAM-BOILERS 


separating  surface  and  to  prevent  priming.     The  tubes  should  be 
always   arranged    in  vertical   and   horizontal    rows,   and   not    be 


SECTION  THROUGH  CHIMNEY  FLUE 

FIG.  19a. — Section  of  Galloway 
Boiler,  Fig.  19. 


DETAIL  OF  WALLS  WHEN  BOILER  IS  SET 
AGAINST  WALL  OF  BUILDING 

FIG.  196. — Section  of  Galloway 
Boiler,  Fig.  19. 


3^g£  ;S«^ 

*?^i^lJ!^S4S§sii  '  - 


CROSS  SECTION-  ONE  BOILER  SET  ALONE, 

FIG.  19c. — Section  of  Galloway 
Boiler,  Fig.  19. 


DETAIL  OF  MIDDLE  WALL  WHEN  BOILERS 
ABE  SET  IN  A  BATTERY 

FIG.  IQd. — Section  of  Galloway 
Boiler,  Fig.  19. 


staggered.     The  horizontal  spacing  is  generally  made  wider  than 
the  vertical,  to  facilitate  the  rising  currents  carrying  the  steam- 


BOILERS   AND  STEAM-GENERATORS 


95 


96 


STEAM-BOILERS 


bubbles.     When  boilers   are  set  fore  and  aft  on  shipboard,  some 
designers  arrange  the  tubes  so  that  the  rows  slope  from  the  centre 


FIG.  20a. — Lancashire  Boiler.     Front 
Elevation. 


FIG.  206.— Lancashire  Boiler. 
Section  at  A  A. 


FIG.  20c. — Lancashire  Boiler. 
Section  at  BE. 


FIG.  20d.— Lancashire  Boiler. 
Section  at  CC. 


toward  each  side,  that  they  may  not  be  lifted  out  of  the  water 
when  the  vessel  rolls  in  a  seaway. 

In  order  to  lighten  the  boiler  by  relieving  it  of  the  necessarily 
heavy  through-stays  in  the  steam-space,  the  heads  above  the  tube- 
line  are  sometimes  curved  inward  over  a  long  radius  (Fig.  22). 


BOILERS   AND   STEAM-GENERATORS 


97 


It  is  always  best  to  flange  the  back  end  of  the  furnace  to  meet 
the  tube-sheet  of  the  combustion-chamber,  so  as  to  keep  the  rivet- 
heads  out  of  the  fire  (Figs.  21  and  22).  With  this  arrangement  it 
is  difficult  to  remove  a  furnace  unless  it  be  especially  flanged  to  pass 
out  of  the  hole  in  the  front  head.  If  the  furnace  end  is  straight  with 
the  flange  on  the  tube-sheet,  the  rivets  should  be  half-countersunk. 


£f 

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FIG.  21. — Scotch  Boiler,  single-ended,  with  common  combustion-chamber. 

The  sides  and  bottom  of  the  combustion-chamber  are  made 
parallel  to  the  shell,  and  should  be  spaced  away  from  the  shell  by 
not  less  than  3  inches  in  the  clear,  although  4  or  5  inches  would  be 
preferable.  The  back  sheet  of  the  combustion-chamber  may  be 
parallel  to  the  back  head,  in  which  case  it  should  be  spaced  away  by 
not  less  than  4  inches  in  small  boilers,  nor  less  than  5  inches  in  large 
ones,  while  6  inches  is  to  be  preferred  in  all  cases.  A  more  expen- 


98 


STEAM-BOILERS 


sive  but  better  method  is  to  slope  the  back  sheet  away  from  the 
back  head,  leaving  a  space  of  about  4  or  5  inches  at  the  bottom  and 
of  8  or  10  inches  at  the  top.  The  top  of  the  combustion-chamber 
may  be  flat,  in  which  case  it  must  be  supported.  This  is  done  by 
girder-stays,  by  crowfoot  stays  to  the  shell,  or  by  girders  strength- 
ened by  stays  to  the  shell.  The  former  method  is  to  be  preferred, 


FIG.  21a. — Scotch  Boiler.     End  view  and  section  of  Fig.  21. 

although  crowfoot  stays  to  the  shell  are  cheaper  and  used  in  many 
cases  with  low  pressures.  The  objection  to  the  combination  girder 
and  stay  to  the  shell  is  the  uncertainty  that  each  will  carry  its  calcu- 
lated stress. 

Care  should  be  taken  to  arrange  the  longitudinal  seams  that 
they  are  not  placed  below  the  furnaces.    The  water  at  the  bottom 


BOILERS  AND   STEAM-GENERATORS 


99 


of  these  boilers  is  apt  to  remain  cold  much  longer  than  that  at  the 
top,  and  seams  located  in  the  bottom  of  the  shell  are  almost  sure  to 
occasion  annoyance  from  leaks.  In  this  particular  hydrokineters 
or  other  devices  for  creating  an  artificial  circulation  are  very  useful. 
These  attachments  consist  of  an  internal  nozzle  through  which 
steam  can  be  blown  from  a  donkey  boiler  or  other  source  of  supply, 


i  i 

FIG.  22. — Scotch  Boiler,  single-ended,  with  separate  combustion-chambers. 


and  thus  form  circulating  currents  during  the  process  of  generating 
steam.  The  cold  feed-water  should  also  enter  at  or  near  the  water- 
line,  so  as  to  assist  the  natural  circulation  and  help  to  maintain 
a  more  uniform  temperature. 

The  smoke-connection  on  the  front  of  the  boiler  may  be  fastened 
to  an  angle  riveted  or  tap-bolted  to  the  boiler-head.  The  sheets 
forming  the  smoke-connection  should  be  arranged  so  as  to  cover 


100 


STEAM-BOILERS 


the  nuts  on  the  ends  of  the  large  stays  in  the  steam-space  and  pro- 
tect them  from  the  corrosive  effect  of  the  gases. 

The  Admiralty  or  Gunboat  Boiler  is  a  modified  form  of  Scotch 
boiler  especially  designed  to  reduce  head-room  and  still  maintain 
heating  surface.  This  is  accomplished  by  decreasing  diameter  and 
increasing  length,  which  necessitates  the  tubes  being  placed  in  line 


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FIG.  22a. — Scotch  Boiler.     End  view  and  section  of  Fig.  22. 

with  the  furnace-flues.  It  has  many  good  features,  but  requires  a 
long  floor-space  (Fig.  24). 

As  the  lower  tubes  are  apt  to  collect  all  the  soot  and  ashes  that 
are  carried  over  the  bridge  wall,  these  tubes  are  sometimes  made  one 
size  larger  than  those  above. 

The  same  general  comments  applicable  to  the  Scotch  boiler  are 
true  for  this  type. 

The  Marine  Boiler  is  the  name  of  a  type  used  on  many  river  and 
sound  steamers  in  America.  It  is  a  very  good  steaming  boiler,  but 


BOILERS  AND   STEAM-GENERATORS 


101 


with  pressures  exceeding  60  pounds  on  the  inch  the  flat  surfaces  are 
objectionable,  and  the  multiplicity  of  stays  makes  it  difficult  to 
inspect  and  clean. 

It  is  internally  fired,  having  a  fire-box  of  the  locomotive  type, 
the  products  passing  through  flues  to  a  back  connection  and  return- 
ing through  tubes. 

As  these  boilers  are  principally  used  with  single-cylinder,  long- 
stroke  engines,  the  steam-space  has  to  be  increased  by  means  of  a 


FIG.  23.— Double-ended  Scotch  Boiler. 


steam-chimney  (Fig.  25),  or  by  a  steam-drum  or  superheater  (Figs. 
26  and  27).  For  high  pressures  the  chimney  is  objectionable,  as  it 
necessitates  the  cutting  out  of  a  large  portion  of  the  shell,  and  in 
consequence  the  steam-drum  is  preferred.  Each  boiler  may  have 
its  own  steam-drum,  or  there  may  be  one  superheater  or  drum  com- 
mon to  all  the  boilers.  The  steam-pipe  connecting  the  boiler  to 
the  drum  is  best  arranged  to  enter  the  side  of  drum  about  one-third 


102 


STEAM-BOILERS 


or  one-quarter  of  its  height  from  the  bottom.  The  steam-pipe  to  the 
engine  should  connect  to  the  opposite  side  and  near  the  top.  There 
should  be  a  small  copper  drain-pipe  to  carry  the  priming  and  con- 
densed steam  from  the  bottom  of  the  drum  back  to  the  boiler. 
This  drain  varies  usually  from  2  to  4  inches  in  diameter.  It  should 
enter  the  shell  of  the  boiler  at  or  just  below  the  water-line,  and 
does  not  require  a  check-valve.  The  steam-connection  to  the  drum 


11 

•*: 
I 

°!                                2"(S  RIVETS 

°,j~o°"o  ViTV         t~18""H^LES"  7°oV 

:- 

SI    i"THICKy         3|  PITCH  ABT. 

r 

Li 


--&ir*sroE  END  PLATES >J 

FIG.  24. — Admiralty  or  Gunboat  Boiler. 


may  enter  the  bottom,  as  in  Fig.  27,  and  be  extended  up  on  the 
inside.  This  particular  design  was  adopted  for  the  sake  of  avoid- 
ing certain  obstructions.  The  side  connection,  as  in  Fig.  26,  is  to 
be  preferred. 

The  piece  forming  the  bottom  of  the  water-legs  of  the  furnaces 
should  be  made  out  of  one  sheet,  flanged  up  solid  around  the  cor- 
ners, or  have  the  corners  welded.  It  should  be  heavier  than  the 
side  sheets.  The  side  sheets  at  the  furnace  should  join  the  curved 
top  of  the  shell  over  the  furnace  in  a  longitudinal  joint  placed  not 
less  than  12  inches  below  the  axis  of  the  cylindrical  part.  The 
throat-piece,  connecting  the  end  of  the  cylindrical  part  to  the  flat 


BOILERS  AND  STEAM-GENERATORS 


103 


furnace  part,  is  the  weakest  piece,  other  things  being  equal,  and 
requires  the  most  care  in  fitting  and  flanging. 

The  width  of  furnace  end  is  usually  equal  to  the  diameter  of 
cylindrical  end  (Fig.  25),  but  may  be  wider  (Fig.  27),  to  increase 


HALF  FRONT  TJf2^ HALF  SECTION 

ELEVATION       MANHOLE  THROUGH  FLUE 

15X11 

FIG.  24a. — Admiralty  or  Gunboat  Boiler. 
Sections  of  Fig.  24. 


FIG.  25a. — Front  end  and  section 
of  Fig.  25. 


the  grate  surface.  The  bridge  wall  may  be  built  of  moulded  fire- 
clay or  bricks,  or  be  constructed  as  part  of  the  boiler  and  then 
called  a  "wet  bridge." 

The  boiler  is  supported  on  iron  saddles  cast  to  fit  both  the  round 
of  the  cylindrical  part  and  the  base  of  the  water-legs. 

The  Locomotive  Boiler  is  one  of  very  convenient  form  and  is 
entirely  self-contained.  It  has  been  used  in  a  variety  of  places  and 


104  STEAM-BOILERS 

has  proved  very  satisfactory.  Its  chief  objection  is  the  flat  sides  oi 
the  fire-box,  necessitating  stays,  but  this  objection  is  true  for  many 
other  types  (Fig.  28). 

In  locomotive-engine   work  the   tubes   are   generally  made  2 
inches  in  diameter,  in  order  to  secure  the  required  heating  surface, 


FIG.  25. — Marine  Boiler  with  steam-drum. 

and  are  spaced  staggered.  The  small  tubes  are  permissible  on 
account  of  the  powerful  draft  produced  by  the  exhaust  from  the 
cylinders.  The  staggering  of  the  tubes  does  not  appear  to  interfere 
with  the  free  steaming  of  the  boiler,  probably  due  to  the  rocking  of 
the  machine  as  it  runs  on  the  track,  which  helps  to  free  the  steam- 
bubbles  from  the  heating  surfaces. 

The  minimum  thickness  of  the  tube-sheet  is  J-inch.     American 
practice  uses  steel  for  the  fire-box  side  and  tube-sheets,  but  some 


BOILERS  AND   STEAM-GENERATORS 


105 


foreign  engineers  still  prefer  copper.  There  appears  to  be  less 
advantage  in  copper  than  would  naturally  be  credited  to  its  high 
conducting  power,  especially  for  the  tube-sheet.  Copper  fire-boxes 
have  to  be  made  thicker  than  steel,  and  the  tube-sheet  is  addi- 
tionally thickened  in  the  tube-space  so  as  to  give  the  tubes  a 
firm  hold.  The  water-legs  are  about  3  inches  in  the  clear. 


2  BUTT  STRAPS -^  EACH 


152-  3  OUTS.DIAM.TUBE&  do.9    B.  W.  G. 


ABT.I12     LENGTH  OF *<    COFJUGATED  FURNACE > 


FIG.  26. — Scotch  Boiler  with  steam-drum. 

This  type  is  a  very  convenient  one  for  portable  boilers,  is  self- 
contained  and  easily  mount  able  on  wheels  or  skids.  These  porta- 
ble boilers  are  often  made  with  a  water-bottom  under  the  ash-pit. 
The  tubes  are  usually  2^  or  3  inches  in  diameter. 

The  Compound  Boiler  is  an  attempt  to  combine  the  advantages 
of  the  fire-  and  water-tubular  types.  It  has  many  promising 


106 


STEAM-BOILERS 


features,  but  creates  complication  and  is  neither  one  thing  nor  the 
other.  At  the  present  time  no  form  has  met  with  what  could  be 
termed  a  commercial  success,  although  some  have  been  reported  as 
giving  satisfactory  results. 

The  Water-tubular  Class  of  boiler  was  created  by  the  continued 
and  well-founded  demand  for  high  pressures  of  steam,  which  neces- 
sitated parts  of  great 
thickness  in  the  older 
types.  In  this  class 
of  boiler  the  water 
is  contained  in  ele- 
ments of  compara- 
tively small  size, 
which  reduces  the 
thickness  of  metal, 
the  quantity  of  water 
contained  and  con- 
sequently the  total 
weight  of  the  boiler ; 
and  increases  the 
rapidity  with  which 
steam  can  be  gener- 
ated without  injury 
from  unequal  expan- 
sion. 

The  early  at- 
tempts were  failures, 
and  many  of  the 
present  designs  can- 
not be  commended, 
better  ones,  are  manu- 


J  0  DIAM  COPPER 
IN  PIPE  fc'THICK 


{*  BENT  PLATE 


FIG.  26a.— Scotch  Boiler. 
End  view  and  section  of  Fig.  26. 


Nearly  all  the  forms,  and  especially  the 
f  actured  solely  by  certain  companies  under  letters  patent,  and  the 
engineer  is  not  called  upon  to  furnish  designs,  but  simply  to  deter- 
mine the  selection  most  suitable  for  his  work. 

Literature  is  full  of  discussion  on  water-tubular  boilers,  and  as 
the  subject  has  not  been  reduced  to  fixed  conditions,  reference  is 
made  to  articles  on  the  subject  already  in  print.  Many  of  such 
articles  will  be  found  in  the  Transactions  of  the  naval  engineering 
societies,  but  those  written  by  manufacturers  and  interested  parties 


107 


108 


STEAM-BOILERS 


should  be  read  with 
some  caution.  The 
weights  are  nearly 
always  underesti- 
mated, and  the 
actual  weight  of 
boiler,  brickwork 
and  setting  or  cas- 
ing make  the  com- 
pleted boiler  much 
heavier  than  is 
usually  stated. 

The  class  has 
been  hampered  by 
many  poor  designs, 
which  have  failed 
and  caused  dis- 
trust, but  general 
condemnation 
should  not  be 
based  alone  on 
these  experiences. 

All  things  con- 
sidered, there  is  no 
reason  why  the 
w  a  t  e  r-t  u  bu  1  a  r 
boiler  should  not 
be  the  boiler  of 
the  future,  and 
such  boilers  are  in 
extensive  use  for 
both  stationary 
and  marine  work. 
They  are  more 
complicated,  as  a 
general  thing,  than 
some  of  the  forms 
o  f  fire-tubular 
boilers,  and  under 


BOILERS   AND   STEAM-GENERATORS 


109 


best  conditions  for  each  have  not  shown  any  particular  increase  in. 
economy.  In  short,  the  two  types  are  about  equal  in  efficiency 
when  placed  under  conditions  suitable  for  each. 

The  water-tubular  class  is  claimed  to  be  the  safer  from  explosion, 
due  to  the  lesser  amount  of  water  contained.  It  is  no  doubt  true 
that  explosions  with  water-tubular  boilers  are  less  destructive. 

The  general  principles  of  boiler  construction  are  as  true  for  water- 
tubular  boilers  as  for  fire-tubular.  It  does  not  appear  necessary  to 


|< 7-7-" OVER  TiHROAT >) 


I 

|< 5CT 

FIG.  28cr. — Locomotive  Boiler.     Sections  of  Fig.  28. 

make  the  tubes  curved  or  bent  in  order  to  allow  for  expansion,  as 
many  straight-tube  boilers  have  proved  satisfactory,  and  straight 
tubes  are  certainly  simpler  and  easier  to  inspect  and  clean. 

Water-tube  boilers  as  a  class  are  capable  of  being  forced  to  high 
rates  of  combustion  without  serious  injury.  When  so  used,  how- 
ever, the  tubes  burn  away  faster  than  the  drums  and  finally  give 
out  completely,  so  that  a  new  set  of  tubes  has  to  be  furnished.  The 
sheet-metal  casings  are  apt  to  get  very  hot,  even  though  the  casing 
be  lined  with  some  non-conducting  material.  In  consequence  con- 
siderably more  heat  is  lost  by  radiation  than  with  the  brick-set  or 
internally  fired  fire-tubular  boilers. 

The  heat-absorbing  value  of  the  tube  surfaces  varies,  and  no 
doubt  many  parts  of  the  same  tube  are  of  little  value  compared  to 
other  parts.  For  good  economy  in  absorbing  the  heat  and  reducing 


110  STEAM-BOILERS 

the  temperature  of  escaping  gases,  the  ratio  of  heating  to  grate 
surface  should  always  be  large. 

As  steam  can  be  raised  in  a  much  shorter  time  (about  one-eighth 
to  one-tenth)  by  using  a  water-tubular  boiler, -there  results  a  con- 
siderable saving  in  fuel  when  the  boilers  have  to  be  frequently 
started. 

A  water-tubular  boiler,  made  up  with  cylindrical  surfaces  of 
small  diameter,  with  heads  bumped  or  of  such  form  as  not  to  require 
staying,  is  certainly  a  step  toward  an  ideal  form.  The  multiplicity 
of  parts  and  joints  is  an  objection,  partially  offset  by  the  absence  of 
stays.  Some  of  the  water-tube  forms  have  departed  from  the  ideal, 
and  nothing  has  been  gained  except  in  the  eyes  of  the  maker.  The 
failure  of  water-tube  boilers  through  unskilled  use  has  raised  the 
question  of  length  of  service,  but  there  is  lack  of  positive  knowledge 
to  prove  that  they  will  not  last  as  long  as  other  forms.  It  has  been 
shown,  however,  that  water-tube  boilers  require  more  constant 
watching  and  care  than  fire-tubular  ones,  owing  to  the  smaller 
quantity  of  water  contained  and  to  their  sensitiveness  to  respond 
to  sudden  changes  of  temperature. 

A.  E.  Seaton  stated  the  requirements  for  a  water-tubular  boiler 
before  the  Institute  of  Civil  Engineers  (London,  May,  1897)  in  the 
following  language : 

"The  ideal  boiler  referred  to — or  perhaps  preferably  the  boiler 
of  the  future,  because  it  is  not  likely  that  any  boiler  will  ever  quite 
fulfil  every  requirement  of  an  ideal  boiler — must  have  a  rapid, 
uniform  and  definite  circulation,  the  upcast  tubes  should  be  very 
considerably  inclined  from  the  horizontal,  and  the  nearer  they  are 
to  the  vertical  position  the  better;  they  may  be  large  or  small,  ac- 
cording to  fancy  or  circumstances;  they  should  be  capable  of  easy 
examination,  and  therefore  must  be  straight  or  nearly  so,  and  their 
arrangement  should  be  such  that  any  one  of  them  may  be  easily 
drawn  and  replaced;  the  downcast  pipes,  or  those  from  the  steam- 
drum  to  the  water-pockets,  should  be  as  direct  as  possible  and  of 
considerable  size,  and  at  or  near  their  bottoms  there  should  be  a 
receptacle  with  no  circulation — in  other  words  a  dead  end,  so  that 
solid  matter  can  be  separated  by  gravity  from  the  liquid;  the 
fireplace  and  its  surroundings  should  be  of  such  size  and  nature 
as  to  allow  of  the  proper  combustion  of  the  fuel  and  its  effluent 
gases,  while  the  general  structure  of  the  boiler  should  be  such  as  to 


BOILERS  AND  STEAM-GENERATORS  111 

enable  it  to  bear  sudden  expansion  and  contraction  with  impunity, 
and  the  whole  of  the  surface  exposed  to  flame  and  hot  gases  should 
be  accessible  for  cleaning.  If  these  conditions  are  fulfilled,  there  is 
no  absolute  necessity  for  using  pure  fresh  water,  inasmuch  as  the 
rapidity  of  flow  will  prevent  deposition  on  the  upcast  pipes  by  the 
mechanical  scour  of  the  water;  the  dead  ends  permit  of  the  deposit 
at  a  safe  place,  and  if  there  is  any  deposit  on  the  downcast  pipes, 
they — being  of  considerable  size  and  easy  of  access — can  be  cleaned 
when  opportunity  serves,  and  if  necessary  would  go  for  a  con- 
siderable period  without  cleaning." 

George  W.  Melville,  U.S.N.,  has  placed  the  advantages  and  dis- 
advantages as  follows  (Trans.  Soc.  Naval  Arch,  and  Marine  Engs., 
Nov.  1899) : 

ADVANTAGES. 

Less  weight  of  water. 

Quicker  steamers. 

Quicker  response  to  change  in  amount  of  steam  required. 

Greater  freedom  of  expansion. 

Higher  cruising  speed. 

More  perfect  circulation. 

Adaptability  to  high  pressures. 

Smaller  steam-pipes  and  fittings. 

Greater  ease  of  repair. 

Greater  ease  of  installation. 

Greater  elasticity  of  design. 

Less  danger  from  explosion. 

DISADVANTAGES. 

Greater  danger  from  failure  of  tubes. 

Better  feed  arrangements  necessary. 

Greater  skill  required  in  management. 

Units  too  small. 

Greater  grate  surface  and  heating  surface  required. 

Less  reserve  in  form  of  water  in  boiler. 

Large  number  of  parts. 

Tubes  difficult  of  access. 

Large  number  of  joints. 

More  danger  of  priming. 


112 


STEAM-BOILERS 


BOILERS   AND  STEAM-GENERATORS  113 

It  is  a  difficult  problem  to  make  a  selection  between  the  two 
types.  Where  quick  steaming  and  wreight  are  prerequisite  the 
water-tubular  class  is  to  be  preferred,  as  also  when  very  high  pres- 
sures and  hard  forcing  are  necessary.  When  these  requirements  are 
lacking  the  choice  becomes  much  more  even,  with  a  slight  tendency 
to  favor  the  fire-tubular  class  as  being  less  complicated.  Water- 
tubular  boilers  usually  have  a  number  of  small  accurately  fitted 
parts,  many  of  which  are  of  special  manufacture,  a  fact  which  is  a 
disadvantage.  Of  the  water-tubular  class  the  straight-tube  type 
are  generally  preferred,  and  practically  tubes  2  inches  diameter 
and  larger  are  better  than  those  smaller  than  2  inches  diameter. 

For  sake  of  illustration  only  a  few  examples  need  be  described. 

The  Babcock  and  Wilcox  Boiler  (Figs.  29  and  29a)  is  one  of  the 
best  known  of  its  particular  kind,  is  simple  in  design,  and  possesses 
strength,  reliability  and  tightness.  The  tubes  have  expanded  ends, 
and  carry  baffles  to  deflect  the  gases  so  as  to  reach  all  the  heating 
surfaces. 

The  Stirling  Boiler  (Fig.  30)  is  of  the  bent-tube  class  and  has 
proved  very  satisfactory.  The  tubes  are  difficult  to  examine  and 
not  especially  easy  to  replace. 

The  Almy  Boiler  (Fig.  31)  is  chiefly  used  for  small  installations 
in  marine  work.  It  has  been  very  successful,  but  is  complicated  by 
having  many  parts,  necessitating  a  number  of  joints.  It  lacks 
facility  for  cleaning,  although  it  has  proved  tight  and  durable. 

The  Niclausse  Boiler  (Fig.  32)  is  moderately  simple,  but  requires 
accurate  fitting.  The  boiler  is  not  self-draining,  but  the  parts  are 
all  accessible  for  cleaning  and  repairing. 

The  Belleville  Boiler  (Fig.  33)  is  of  French  design,  and  has 
become  widely  known  through  its  marine  use.  It  has  not  proved 
entirely  satisfactory,  probably  due  to  the  trouble  to  maintain  it 
in  good  working  order.  It  requires  considerable  skill  in  firing  and 
handling,  and  the  design  is  somewhat  complex. 

The  Thornycroft  Boiler  (Fig.  34)  is  capable  of  withstanding  a 
high  degree  of  forcing.  The  bent  tubes,  however,  make  it  difficult 
to  clean  and  practically  impossible  to  inspect  internally. 

The  Yarrow  Boiler  (Fig.  35)  is  very  simple  and  easy  to  clean  and 
inspect.  The  tubes  are  difficult  to  replace,  and  their  rigidity  has 
been  criticised.  The  tubes  are  generally  small,  about  1J  inches  to 
1}  inches  diameter. 


114 


STEAM-BOILERS 


BOILERS  AND   STEAM-GENERATORS 


115 


To  Proportion  a  Boiler  to  Perform  a  Required  Duty.  Usually 
every  engineer  has  his  own  ideas  how  to  proceed  to  proportion 
a  boiler  or  battery  of  boilers  to  meet  certain  requirements,  but 
the  various  methods  can  be  reduced  to  the  three  following  schemes. 


kV-^:?.5£.y:^^ 

FIG.  30. — Stirling  Boiler. 

If  any  one  be  used,  it  is  well  to  check  the  result  by  one  of  the 
others. 

1.  Determine  the  weight  of  water  to  be  evaporated  per  hour. 
This  should  be  the  maximum  and  not  the  average  weight,  when 
variable  loads  are  expected.  This  can  be  done  by  assuming,  when 
the  type  of  engine  is  known,  the  steam  consumed  per  indicated 
horse-power  hour  and  multiplying  by  the  required  horse-power. 


116 


STEAM-BOILERS 


For  steam-heating  plants  it  must  be  calculated  from  the  radiating 
surface.  (See  works  on  that  subject.)  For  industrial  uses  it 
must  be  obtained  by  experience.  In  all  cases  care  must  be  exer- 
cised to  see  that  all  auxiliary  engines  and  other  users  of  steam  are 
included. 


FIG.  31.— Almy  Boiler. 

Knowing  the  class  of  fuel,  the  evaporation  per  pound  of  fuel  can 
be  assumed,  and  dividing  the  first  result  by  this  rate  of  evaporation, 
the  total  weight  of  fuel  can  be  determined.  See  that  both  total 
water  evaporated  and  rate  are  either  " actual"  or  "from  and  at 
212°."  Having  thus  determined  the  total  fuel,  the  grate  area  can 
be  calculated  or  assumed,  and  the  height  of  chimney  assumed  or 
calculated  for  the  required  rate  of  combustion.  Having  deter- 


BOILERS  AND   STEAM-GENERATORS 


117 


mined  the  grate  area,  the  heating  surface  can  be  proportioned 
from  the  principles  stated  under  Heating  Surface. 

2.  Knowing  the  class  of  engine  to  be  used,  assume  the  amount 
of  heating  surface  per  horse-power.     This  can  only  be  done  after 


FIG.  32.— Niclausse  Boiler. 

considerable  experience  has  been  attained,  or  by  comparison  with 
some  similar,  successful  plant. 

Multiply  by  the  total  horse-power  required  and  the  product  will 
be  total  heating  surface.  Remember  that  maximum  and  not 
average  horse-power  must  be  used,  including  the  power  of  all  auxil- 
iary engines.  The  grate  surface  can  be  determined  by  the  prin- 
ciples stated  above. 

3.  Assume  a  coal  consumption  per  horse-power  per  hour,  and 


118 


STEAM-BOILERS 


then  determine  the  total  coal  to  be  used  by  multiplying  by  maxi- 
mum horse-power.     Assume  or  calculate  the  rate  of  combustion 


per  square  foot  of  grate  per  hour.     Divide  total  amount  of  coal  by 
this  rate,  and  the  quotient  will  be  area  of  grate  required.     Then 


BOILERS  AND  STEAM-GENERATORS  119 

proportion  amount  of  heating  surface  as  before,  and  make  the  stack 
high  enough  to  give  the  rate  of  combustion. 

The  first  method  is  generally  the  safest,  but  it  is  well  to  check 
the  results. 

After  having  fixed  the  general  proportions,  the  number  of 
boilers  must  then  be  determined.  Remember  that  it  is  always 


FIG.  34.— Thorny  croft  Boiler. 

more  economical  to  have  ample  boiler  capacity,  so  as  not  to  have 
to  force  beyond  the  normal  rating. 

It  is  wise  and  in  most  cases  absolutely  essential,  especially  when 
the  plant  is  in  steady  operation,  to  have  a  surplus  boiler,  so  that 
any  one  can  be  shut  down  for  cleaning  and  repairs  without  affecting 
the  plant. 


120 


STEAM-BOILERS 


While  it  is  possible  to  calculate  the  size  of  boiler  required  by 
using  the  heat-units  contained  in  the  steam  and  in  the  coal,  making 
allowance  for  the  efficiency  of  the  boiler,  it  is  just  as  safe  in  practice 
to  use  the  three  methods  given,  as  so  many  assumptions  have  to 
be  made  in  every  case. 


FIG.  34a. — Front  view  and  section  of  Fig.  34. 


Steam-space.  The  contents  of  a  boiler  are  divided  into  water- 
space  and  steam-space.  The  former  needs  to  be  of  only  such 
capacity  as  safely  to  contain  the  water  necessary  for  the  generation 
of  the  steam.  In  water-tube  boilers  the  water-space  is  very  small 


BOILERS  AND   STEAM-GENERATORS 


121 


compared  to  many  of  the  fire-tube  boilers.  In  the  latter  the  water- 
space  has  to  be  large,  due  to  the  design,  so  that  there  may  be  little 
danger  of  uncovering  the  highest  heating  surfaces. 

The  steam-space  must  vary  in  capacity  due  to  the  demand  for 
steam;  the  smallest  space  being  required  for  steady  outflows  of 
steam,  and  the  largest  for  those  that  are  intermittent. 

For  very  intermittent  flows,  as  the  demands  for  steam  by  engines 
of  long  stroke  making  few  turns  per  minute,  the  space  is  frequently 


FIG.  35. — Yarrow  Boiler. 

figured  in  terms  of  the  cylinder  capacity.  Thus  for  the  walking- 
beam  class  of  engine,  as  found  on  American  river  steamers,  often 
having  a  single  cylinder  50  inches  diameter  by  10  feet  stroke,  with 
steam  at  30  to  50  pounds,  the  steam-space  is  about  four  times  the 
cylinder  capacity.  Occasionally  from  3  to  3^  times  has  been  found 
sufficient. 

Table  XIII.  gives  results  based  on  practice,  and  is  in  the  main 
taken  from  " Marine  Engineering"  by  Seaton.  It  may  be  found 
that  experience  will  modify  the  figures  in  estimating  the  required 
space  for  given  conditions.  The  space  does  not  depend  on  pressure, 
but  on  the  volume  of  steam  required.  For  uses  other  than  for 
steam-engines  the  space  can  only  be  determined  by  experience. 

With  economical  triple-expansion  .  engines  and  quadruple- 
expansion  engines  the  steam-space  may  be  reduced  15  to  20  per  cent. 

When  mechanical  draft  is  used  the  space  may  be  reduced  25 
to  50  per  cent,  according  to  circumstances. 

Priming.  When  ebullition  is  violent  the  bubbles  of  steam  rise 
with  such  rapidity  as  to  keep  the  water  surface  continually  broken, 
and  in  consequence  a  considerable  quantity  of  water  in  small 


TABLE  XIII 
STEAM-SPACE;    NATURAL  DRAFT 


General  Type  of  Engine. 


Per  I.  H.  P.  in 
Cubic  Feet. 


Small  slow-running  engines,  steam-pumps,  etc. 

Moderately  slow-running  engines 

Faster-running  engines 

Marine  paddle-engines,  direct-connected 

Marine  walking-beam  engines 

Fast-running  stationary  engines 

Marine  engines,  vertical  direct-acting 

Naval  and  fast-running  marine  engines 


1.00  to  2. 50 

1.00 
1.00  to  0.80 

0.80 

0.80  to  1.00 
0 . 50  to  0 . 80 

0.65 
0.55  toO. 65 


particles  is  carried  up  with  the  steam  and  retained  in  mechanical 
suspension.  This  action  is  called  " priming"  or  "foaming."  If 
there  be  no  quiet  place  in  the  steam-space  for  this  priming  water  to 
settle  or  separate  from  the  steam,  it  is  carried  over  into  the  steam- 
pipe  and  is  liable  to  cause  serious  damage  to  the  engine  by  knocking 
off  the  cylinder-heads  or  disarranging  the  valves.  Unless  super- 
heating or  steam-heating  surfaces  be  provided,  nearly  all  boilers 
will  pass  off  with  the  steam  some  priming  or  entrained  water. 
Steam  containing  less  than  2^  per  cent  moisture  may  be  said  to  be 
"  commercially  dry." 

Priming  or  foaming  may  be  caused  by  dirty  or  greasy  water,  oil 
in  the  boiler,  etc.,  but  it  is  often  produced  by  the  design,  or  by 
forcing  a  boiler  beyond  its  proper  capacity.* 

When  the  steam-space  is  too  small  there  is  a  fall  in  pressure  at 
each  efflux  of  steam,  which  will  cause  sudden  and  rapid  ebullition. 
Priming  from  this  cause  can  only  be  prevented  by  enlarging  the 
steam-space,  or  by  contracting  the  area  of  steam-pipe.  This  latter 
alternative  may  reduce  the  general  efficiency  of  the  engine  by  lower- 
ing the  initial  pressure,  but  must  often  be  resorted  to  in  order  to  save 
the  great  expense  of  condemning  a  boiler  already  built. 

Priming  is  more  often  caused  by  the  conformation  of  the  boiler 
than  by  contracted  steam-space.  If  the  water-line  in  a  shell  be  high, 
the  flatness  of  the  sides  will  cause  priming,  by  tending  to  contract 
the  effective  water-separating  surface,  and  by  preventing  a  proper 
downward  current  without  interfering  with  the  upward  current. 

There  are  no  special  rides  for  area  of  water  surface,  as  the  value 

*  Boilers  which  often  steam  quietly  with  bad  waters,  sometimes  foam 
when  a  change  of  water  is  introduced,  probably  due  to  the  new  water  dis- 
solving some  of  the  deposit.  Carbonate  of  sodium  may  cause  foaming  for 

a  like  reason. 

122 


BOILERS  AND  STEAM-GENERATORS  123 


of  the  area  depends  less  on  the  quantity,  by  volume  or  weight,  of 
steam  generated  than  on  the  general  design. 

The  design  should  provide  for  the  following  conditions  in  order 
to  prevent  priming: 

First.  Use  of  clean  water.  If  the  feed  comes  from  a  surface 
condenser,  the  oil  from  the  cylinder  lubricators  should  be  sepa- 
rated or  extracted. 

Second.  Sufficient  steam-room  to  prevent  fluctuation  in  pres- 
sure. 

Third.  As  great  a  water  surface  as  possible,  so  that  the  sepa- 
ration of  steam  may  be  least  violent. 

Fourth.  The  water  surface  should  cover  not  less  than  one-half 
of  the  area  of  each  space  left  for  downward  currents.  This  is 
most  important. 

Fifth.  The  steam-pipe  should  connect  as  high  above  the  water- 
level  as  possible,  and  not  directly  over  the  hottest  part.  In  boilers 
having  comparatively  small  steam-space  a  collecting-pipe  or  dry- 
pipe,  so  placed  on  the  inside  and  connected  to  the  steam-pipe  as 
to  draw  steam  from  all  parts,  will  be  found  a  good  device.  Such 
a  pipe,  frequently  called  an  "  anti-priming  "  pipe,  should  be  stopped 
at  the  ends  and  have  holes  or  slots  on  its  upper  side  only.  There 
should  be  a  drain  on  under  side.  Baffle-plates  may  also  be  used 
inside  the  boiler,  so  arranged  as  to  make  it  difficult  for  moisture 
to  pass. 

Sixth.  The  area  of  steam-pipe  should  not  be  made  too  large 
for  the  capacity  of  the  boiler. 

Some  engineers  proportion  the  water  surface  so  that  the  velocity 
of  steam  rising  from  it  shall  not  exceed  2^  feet  per  second.  If 
the  velocity  be  greater,  priming  is  almost  sure  to  occur,  as  when 
once  formed  the  water  particles  will  have  difficulty  in  settling 
back  against  a  current  of  even  less  than  half  that  velocity. 

Thus,  let  V  denote  the  cubic  feet  of  steam  generated  per  second, 
and  S  denote  the  minimum  water  disengaging  surface  in  square 
feet.  Then 


In  water-tubular  boilers  the  water  surface  can  be  very  mate- 
rially reduced  below  the  area  required  in  fire-tubular  boilers  and  still 
furnish  dry  steam. 


124  STEAM-BOILERS 

Just  how  small  the  surface  may  be  depends  on  the  design,  which 
is  an  all-important  factor  in  this  particular  in  all  water-tubular 
boilers.  The  least  amount  can  be  determined  only  by  experience. 

In  completing  the  design  it  will  often  be  found  that  all  the  sug- 
gestions made  in  this  chapter  cannot  be  provided  for.  In  such 
cases  the  design  should  be  altered  so  as  to  retain  the  more  important 
ones,  and  none  of  the  suggestions  should  be  discarded  except  after 
careful  study  and  on  the  exercise  of  best  judgment. 


CHAPTER  VI 
CHIMNEY-DRAFT 

Problem  of  Gravitation.  Theory  of  Peclet  as  expressed  by  Rankine. 
Natural  Draft.  Rate  of  Combustion.  Author's  Experience.  Area  and 
Height  of  Chimney. 

BEFORE  any  final  calculations  can  be  made  for  the  general  design 
the  intensity  of  the  draft  must  be  considered,  since  upon  it  depends 
primarily  the  performance  of  a  boiler.  The  quantity  of  fuel  that  can 
be  burned  is  governed  by  the  draft,  which  determines  the  rate  at 
which  the  air-supply  is  drawn  into  the  furnace.  The  quantity  of 
air  that  will  thus  be  drawn  through  the  grate  is  chiefly  controlled 
by  the  area  of  the  flue,  the  height  of  the  chimney  and  the  tempera- 
ture of  the  gases  of  combustion  in  excess  of  that  of  the  outside  air. 
Other  things  being  equal,  the  velocity  of  the  ascending  current  of 
hot  gas  may  be  taken  as  varying  directly  as  the  square  root  of  the 
height  of  the  chimney. 

The  problem  of  chimney-draft  is  really  one  of  gravitation,  and 
not  of  thermodynamics.  No  doubt  heat  must  be  supplied  in 
order  to  maintain  the  velocity  of  the  gases,  but  that  same  velocity 
is  due  not  to  the  heat  per  se,  but  to  the  difference  in  weight  of  the 
hot  gases  and  the  cold  outside  air.  For  a  full  discussion  of  the 
subject,  reference  is  made  to  papers  in  the  Transactions  of  the 
American  Society  of  Mechanical  Engineers,  Volume  XI,  1890. 

The  best  accepted  theory  is  that  of  Peclet,  which  is  admirably 
expressed  by  Rankine  briefly  as  follows: 

The  draft  of  a  furnace  or  the  quantity  of  mixed  gases  that  it  will 
discharge  in  a  given  time  may  be  estimated  either  by  weight  or  by 
volume.  It  is  often  expressed  by  the  pressure  required  to  produce 
the  current.  This  pressure  is  usually  stated  in  "  ounces  per  square 
inch"  or  in  "inches  of  water." 

In  order  to  facilitate  the  discussion  it  may  be  assumed  without 
serious  error  for  all  practical  purposes,  that  the  volume  of  the  gases 

125 


126  STEAM-BOILERS 

of  combustion  at  any  temperature  is  equal  to  the  volume  of  the  air 
supplied  when  taken  at  the  same  temperature. 

The  volume  at  32°  F.  of  the  gases  may  be  assumed  at  12.5  cubic 
feet  for  each  pound  of  air  supplied  to  the  furnace. 

Volume  at  32°  F.  per 
Per  Pound  of  Fuel.  Pound  of  Fuel 

When  12  pounds  of  air  are  supplied  ........  150  cubic  feet 

lt      ic        il        ft    ((     «  <( 


The  volume   at  any  other  temperature,  such  as  T°,  may  be 
calculated  from  the  formula 


Volume  at  r°=  7  =  Vol.  at  32°X 


The  following  results  were  obtained  by  this  formula,  and 
intermediate  results  may  be  interpolated  with  sufficient  accuracy 
for  practical  work. 

Supply  of  Air  in  Pounds  per  Pound  Fuel. 
Temp,  of  Gases.  12  18  24 

Volume  of  Gases  per  Pound  Fuel  in  Cubic  Feet. 

1112°  F.  479  718  957 

752°  369  553  738 

572°  314  471  628 

392°  259  389  519 

Let  w   denote  weight  of  fuel  burned  in  furnace  per  second. 

"   V0      "  volume  at  32°  F.  of  air  supplied  per  pound  of  fuel. 

"   TJ  "  absolute  temperature  of  gas  discharged. 

"   T0  "            "                  "            corresponding  to  32°  F. 

"A  "  area  of  chimney  in  square  feet. 

"  u  "  velocity  of  the  current  of  gas  in  feet  per  second. 
Then 


u  = 


which  formula  can  be  easily  solved  by  interpolation  from  the  list 

V  r 
of  values  of  —^—  just   given,  when  the  weight  of  coal  burned  is 

To 
known  or  assumed. 


CHIMNEY-DRAFT  127 

Again,  by  transposition,  the  weight  of  fuel  that  may  be  com- 
pletely burned  can  be  calculated  when  the  velocity  of  the  current 
of  hot  gases  is  known  or  assumed,  thus : 

uArn 


The  weight  of  such  a  column  of  hot  gas  may  be  readily  deter- 
mined from  the  following  approximate  formula  : 

Density  in    pounds    per     cubic     foot  =  D  =  —(0.0807+  ^ 

Tl  \  V  0, 

in  which  0.0807  is  the  weight  of  one  cubic  foot  of  air  in  pounds 
at  32°  F. 

Let  I  denote  the  length  of  chimney  and  flue  leading  to  it,  in  feet. 
"   m      "      its  hydraulic  mean  depth,  or  area  divided  by  the 

perimeter. 

"  /        "      a   coefficient  of  friction,  which  for  gases  over  sooty 
surfaces  is  stated  by  Peclet  to  be  about  0.012. 
"  G       "      a  factor  of  resistance  offered  by  the  grate  and 
bed  of  fuel  to  the  passage  of  the  air,  which, 
according  to  Peclet,  has  a  value  of  12  when 
burning   from  20  to  24  pounds    of    coal    per 
square  foot  of  grate  per  hour. 
Then  the  "head"  to  produce  the  draft  is 


The  head,  h,  is  given  in  feet  as  the  height  of  a  column  of  hot  gas, 
just  sufficient  to  produce  the  unbalanced  pressure  which  produces 
the  current,  u. 

This  head  may  be  caused  in  three  ways  : 

1.  By  the  natural  draft  of  the  chimney; 

2.  By  a  jet  or  blast  of  steam  or  air; 

3.  By  a  fan  or  blowing-machine. 

The  head  caused  by  the  natural  draft  of  the  chimney  is  a  column 
of  hot  gas  of  such  a  height  as  to  have  a  weight  equivalent  to  the 
difference  between  those  of  equal  columns  of  cold  air  outside  the 
chimney  and  of  hot  gases  inside  the  chimney  (Fig.  36). 


128 


STEAM-BOILERS 


It  is  more  convenient  to  express  the  outside  column  of  cold 

air  in  feet  of  hot  gas,  that  is, 
in  the  height  of  a  column  of  hot 
gas  having  the  same  weight  as 
the  column  of  cold  air.  This 
is  done  by  computing  the 
weight  of  a  column  of  cold 
air  one  square  foot  in  section 
and  as  high  as  the  top  of 
the  chimney  is  vertically  above 
the  grate,  and  dividing  the  re- 
sult by  the  weight  of  a  cubic 
foot  of  hot  gas.  If  from  this 
result  the  height  of  the  chim- 
ney above  the  grate  be  sub- 
tracted, which  is  the  height 
of  the  hot-gas  column  inside 
the  chimney,  the  difference 
will  be  the  "head,"  h,  which 
causes  the  draft.  Thus 

Let  H  denote  the  height 
of  the  chimney  above  the 
grate. 

Let  r2  denote  the  absolute 
temperature  of  the  external 
air. 

Then 


FIG.  36.— Chimney-draft. 

H  ^(0.0807) 


or 


H= 


From  this  last  equation  can  be  calculated  the  height  of  chimney 
to  produce  a  given  draft. 

It  is  evident  that,  for  a  given  outside  temperature,  there  must 
be  some  other  temperature  for  the  hot  gases  which  will  produce  the 


CHIMNEY-DRAFT  129 

"best"  draft,  that  is,  the  draft  which  will  discharge  the  maximum 
weight  of  gases  in  a  given  time.  The  velocity  of  the  current,  u,  or 
the  strength  of  the  draft,  will  increase  with  the  values  of  rv  but, 
owing  to  the  rarification  of  the  hot  gases,  the  maximum  dis- 
charge in  weight  will  be  at  some  fixed  temperature  for  every  value 
of  T2. 

Since  the  velocity  of  the  current  of  hot  gases  is  proportional  to 
\/h,  it  must  also  be  proportional  to  X/CO.OG^—  T2).     The  density  of 

the  hot  gas  is  proportional  to       .      Also,  the  weight  discharged 

Ti 
per  second  is  proportional   to   the  velocity  times   density,  or   to 


This  expression  becomes  a  maximum  when 


Therefore  the  greatest  weight  of  hot  gas  is  discharged  from  the 
chimney  when  the  absolute  temperature  of  the  hot  gas  in  the 
chimney  is  to  that  of  the  external  air  as  25  is  to  12. 

When  this  condition  is  fulfilled,  h  =  H.  That  is,  for  the  "best" 
chimney-draft,  or  condition  for  maximum  discharge  of  gases  as 
measured  by  weight,  the  head  when  expressed  in  the  height  of  a 
column  of  hot  gas  is  equal  to  the  height  of  the  chimney. 

Since  the  external  air  may  be  taken  as  having  an  average  tem- 
perature of  50°  F.,  equivalent  to  511°.2  absolute,  and  since  the  cor- 
responding temperature  of  chimney-gases  for  maximum  discharge 
would  be  1065°  absolute,  corresponding  to  603°.8  F.,  it  may  be 
stated  that  the  "best"  draft  to  create  a  maximum  discharge  will  be 
produced  when  the  temperature  of  the  gases  in  the  chimney  is 
nearly  sufficient  to  melt  lead. 

2.  When  the  draft  is  produced  by  a  jet  or  blast  in  the  chimney, 
an  artificial  current  is  caused  by  the  impact  of  this  jet  against 
the  hot  gases.     The  head  is  equivalent  to  that  atmospheric  head, 
or  natural  head,  which  would  be  required  to  produce  the  same 
velocity. 

3.  When  the  draft  is  produced  by  a  fan  or  blowing-machine,  the 
effect  is  that  an  artificial  current  is  caused.      The  head,  as  in  the 


130  STEAM-BOILERS 

previous  cases,  is  due  to  the  unbalanced  pressures  between  the 
external  air  and  internal  gases. 

The  conditions  of  artificial  draft  will  be  considered  in  Chapter  XI. 

Natural  Draft.  Experience  with  many  chimneys  of  various 
sizes  has  given  proof  of  the  general  correctness  of  the  analysis  of 
Rankine  and  Peclet.  There  have  been  cases  reported  in  which 
results  differ,  but  such  have  shown,  on  careful  inspection,  either 
an  incorrect  application  of  the  formulae  or  the  introduction  of  con- 
ditions not  properly  accounted  for.  The  chief  difficulty  in  using 
the  Peclet  formulae  is  the  selection  of  proper  values  for  the  constants. 

In  practical  application,  for  the  determination  of  the  height  of 
chimney-stack,  values  for  w,  u,  and  A  must  be  first  settled.  A  value 
for  w  is  determined  by  the  conditions  of  the  new  plant,  since  a 
boiler  or  battery  of  boilers  is  designed  to  evaporate  a  given  amount 
of  water.  This  would  necessitate  the  combustion  of  a  certain 
amount  of  coal  per  second.  The  value  of  A  is  generally  made 
about  one-seventh,  one-eighth,  or  one-ninth  the  area  of  the  grate, 
as  such  proportions  have  given  good  results.  The  larger  values  are 
for  bituminous  coal  or  for  short  stacks,  while  the  smaller  are  for 
anthracite  or  for  tall  stacks.  When  w  and  A  are  assumed,  the 
value  of  u  can  be  calculated.  If  a  value  be  assumed  for  u,  then  w 
can  be  calculated. 

Without  serious  error  for  preliminary  work,  the  expression  — 

can  be  taken  as  unity,  and  a  value  for  h  can  be  easily  determined. 
The  value  of  H,  which  was  to  be  found,  then  depends  on  the  assumed 
temperature  of  the  gases  which  may  be  expected  in  the  proposed 
plant. 

The  frictional  resistance,  /,  must  necessarily  be  a  variable  quan- 
tity, but  probably  does  not  differ  much  in  ordinary  cases  from  the 
value  assigned  by  Peclet.  The  resistance  to  draft,  offered  by  the 
grate'  and  fuel,  G,  is  necessarily  large,  requiring  the  major  part  of 
the  head.  It  is  a  loss  that  is  an  essential  part  of  the  system.  While 
the  value  of  Peclet  was  determined  from  experiments  where  20  to 
24  pounds  of  coal  were  burned  per  square  foot  of  grate  per  hour,  the 
real  value  may  be  somewhat  less  for  lower  rates  of  combustion. 
Some  engineers  use  11  for  rates  of  15  pounds.  The  true  value  must 
depend  not  only  on  the  rate,  but  on  the  thickness  of  fire,  size  of  coal 
and  kind  of  grate. 


CHIMNEY-DRAFT  131 

From  what  has  been  stated  it  will  be  seen  that  in  practical 
application  many  assumptions  have  to  be  made  under  conditions 
which  are  more  or  less  rapidly  changing.  In  consequence  engineers 
are  prone  to  adopt  empirical  rules  for  the  determination  of  their 
results,  and  experience  has  proven  such  methods  sufficiently  accurate 
for  all  practical  cases. 

Furthermore,  attempted  accurate  calculations  are  rendered 
really  approximate  due  to  effects  of  location  of  chimney,  for  which 
no  exact  allowance  can  be  made.  The  draft  will  be  stronger  in 
chimneys  built  on  high  ground  than  in  those  in  valleys ;  or  in  those 
on  open  plains  than  in  those  surrounded  by  high  buildings.  Wind 
also  may  help  the  draft  considerably,  especially  if  the  chimney-top 
be  properly  designed.  For  these  reasons  the  funnels  of  steamers 
always  have  a  better  draft  than  those  of  equal  height  on  land. 

Rate  of  Combustion.  The  rate  of  combustion  primarily  depends 
on  the  strength  of  the  draft,  which  will  vary  approximately,  under 
similar  conditions,  as  the  square  root  of  the  height  of  chimney.  It 
will  also  depend  upon  the  grade  or  quality  of  fuel,  its  dryness,  char- 
acter of  grate,  proportions  of  combustion-chamber,  amount  of  air 
supplied  and  its  initial  temperature. 

The  rate  as  generally  stated  in  text-books  for  various  kinds  of 
boilers  is  given  in  Table  XIV.  See  Rankine's  "  Steam-engine." 

TABLE  XIV 
RATES  OF  COMBUSTION:  NATURAL  DRAFT 


Kind  of  Boiler. 


Pounds  of  Coal 

per  Square  Frot 

of  Grate  Surface 

per  Hour. 


Cornish  boilers,  slowest  rate 

"  "        average  rate 

Factory  boilers,  average  rate 

Marine  boilers,  average  rate 

Ordinary  boilers,  quickest  rate  with  dry  coal,  air  admitted 


under  grate  only, 


Ordinary  boilers,  quickest  rate  with  soft  coal,  with  area  of  air- 


holes above  grate  equal  to  •£•$  area  of  grate. 


4 
10 

12  to  16 
16  to  24 

20  to  23 

24  to  27 


Such  results  were  based  on  the  practice  of  the  time  and  with  the 
usual  height  of  stack  as  then  obtained. 

The  actual  rate  of  combustion  will  depend  on  the  conditions, 
however,  stated  above. 


132 


STEAM-BOILERS 


The  anthracites  require  a  stronger  draft  than  the  bituminous 
coals,  therefore  with  equal  draft-strengths  the  hard  coals  burn  at  a 
lower  rate  than  the  soft  ones. 

Assuming  ordinary  factory  conditions,  the  average  coals  of  the 
various  qualities  may  be  taken  relatively  as  in  Table  XV.  It  must 
be  remembered  that  some  of  the  soft  coals  will  burn  still  more  freely 
than  here  indicated,  while  some  of  the  anthracites  less  rapidly. 
The  figures  must  be  treated  as  averages. 

TABLE  XV 

RELATIVE    RATES    OF    COMBUSTION    FOR    COALS 


Kind  of  Coal. 

Weight  of  Coal 
Burned  per 
Square  Foot 
of  Grate. 

Area  of  Grate 
per  Pound 
Consumed. 

Good  anthracites  

1    00 

1   00 

Good  semi-anthracites  and  bituminous  
Ordinary  low  grades,  soft.  .  .        .    . 

1.15 
1  50 

0.90 
0  70 

hard.      . 

0  90 

1  10 

Restricted  draft  area  will  reduce  the  rate  of  combustion,  and 
too  great  an  area,  within  moderate  limits,  does  not  increase  the  rate 
as  rapidly  as  it  lowers  the  efficiency  of  the  boiler.  The  area  to  give 
best  results  is  entirely  dependent  on  the  character  of  the  coal  and 
on  the  strength  of  the  draft.  For  ordinary,  average  conditions  the 
area  should  be  about  one-eighth  the  area  of  grate. 

Rate  Depends  on  Quality  and  Size  of  Fuel.  All  conditions 
of  chimney,  etc.,  being  the  same,  the  rate  of  combustion  will  vary; 
wood  will  burn  the  fastest,  then  bituminous  coal,  then  semi-bitumi- 
nous, semi-anthracite  and  finally  anthracite.  The  small  sizes  of 
anthracite  will  burn  more  slowly  than  the  larger  ones.  Conse- 
quently for  equal  rates  of  combustion  the  highest  chimney  is  re- 
quired for  the  small  sizes  of  anthracite,  and  the  lowest  for  bituminous 
coals  and  wood. 

The  rate  is  found  to  vary  for  the  different  fuels  with  the  type 
and  setting  of  the  boilers,  those  offering  the  greatest  resistance  to 
draft  will  have  the  lowest  rate.  As  the  variation  for  the  different 
qualities  of  fuel  is  so  irregular,  no  definite  relation  can  be  ex- 
pressed and  much  depends  on  experience. 

Walter  S.  Hutton,  in  "  Steam-boiler  Construction/'  states  rates 
of  combustion  and  draft-pressures  for  various  chimney  heights,  but 


CHIMNEY-DRAFT 


133 


does  not  state  the  exact  conditions.  Table  XVI  gives  his  results, 
as  printed  in  "  Mechanical  Draft,"  Sturtevant  and  Co.  The  same 
table  gives  results  obtained  by  Prof.  W.  P.  Trowbridge  based  on 
uniform  data  for  all,  but  without  allowing  for  variation  in  kind  or 
quality  of  fuel.  See  "Heat  and  Heat-engines/'  by  Trowbridge. 

TABLE  XVI 

RATES    OF    COMBUSTION    FOR    DIFFERENT    CHIMNEY    HEIGHTS 


Pounds  of  Coal  oer 

Pounds  of  Coal  per 

Height  of 
Chimney 
above  Grate, 

Square  Foot  of  Grate 
per  Hour. 

Height  of 
Chimney 
above  Grate, 

Square  Foot  of  Grate 
per  Hour. 

in  Feet. 

in  Feet. 

Hutton. 

Trowbridge. 

Hutton. 

Trowbridge. 

25 

10 

8.5 

100 

22 

19.0 

50 

16 

13.1 

110 

24 

20.0 

60 

17 

14.5 

120 

27 

70 

18 

15.8 

150 

40 

80 

19 

16.9 

200 

60 

90 

20 

18.0 

250 

80 

The   formula   of   William   Kent  (Trans.  Am.  Soc.  Mechanical 
Engineers,  Vol.  VI),  based  on  observation,  is: 


in  which  H  denotes  the  height  of  chimney,  the  area  of  the  chimney 
being  taken  at  one-eighth  of  the  grate.  For  any  ratio  of  grate  to 
area  of  chimney  the  formula  becomes 

AVJJ 
=  0.06  ' 

in  which  A  denotes  area  of  chimney;  F,  the  pounds  of  coal  burned 

per  hour. 

Prof.  R.  H.  Thurston  states  the  following  formula: 

Under  best  conditions,  as  in  marine  work,  with  anthracite  coal, 

Rate  =  2\/#-l. 

Under  more  ordinary  conditions,  as  in  general  stationary  work, 
with  anthracite  coal, 

Rate=1.6V77-l. 


134  STEAM-BOILERS 

Best  Welsh  and  Maryland  semi-anthracite  or  good  bituminous 
coals  should  give 


The  less  valuable  soft  coals  with  air  admitted  above  the  grate, 
in  proportion  of  area  of  holes  to  grate  as  1  to  36,  should  give 


Under  ordinary  conditions  of  stationary  practice  each  10  feet 
additional  height  to  the  chimney  will  increase  the  draft  about  one- 
twelfth  of  an  inch  water-pressure,  and  each  half-inch  of  pressure 
will  increase  the  rate  of  combustion  about  10  pounds  of  coal  per 
hour.  George  W.  Melville,  U.  S.  N.,  states  (Transactions  of  Marine 
Congress,  Chicago,  1894)  that,  based  on  naval  experience,  each 
additional  10  feet  in  height  of  funnel  increased  the  pressure  of  draft 
about  one-eighth  inch,  and  that  a  100-foot  funnel  would  give  a  rate 
of  about  25  pounds  of  coal  per  square  foot  of  grate  per  hour. 

Author's  Experience.  —  From  observations  made  by  the  author, 
the  figures  given  by  Hutton  represent  rates  for  free-burning  bitumi- 
nous coals,  and  those  of  Trowbridge  for  anthracites,  while  both  are 
only  obtained  in  stationary  work  when  everything  is  favorable  for 
rapid  combustion,  open  dampers  and  direct  connections  to  stacks 
without  tortuous  passages  for  the  gases  through  the  boiler.  For 
.similar  reasons,  the  empirical  formulae  are  apt  to  furnish  higher 
values  than  will  be  obtained  in  daily  practice.  Possibly  the  formulae 
and  the  observations  were  based  on  experiments,  where  the  escaping 
gases  were  at  a  greater  temperature  than  is  usually  the  endeavor 
under  present  practice  to  secure.  The  temperature  of  the  gases 
should  be  as  low  as  is  consistent  with  the  requirements  of  draft,  and 
the  draft  should  be  so  regulated  by  proper  design  of  chimney  area 
and  height  as  to  permit  of  the  lowest  possible  temperature. 

In  a  new  design  it  is  always  best  to  have  ample  boiler  power, 
as  losses  are  incurred  when  boilers  are  forced  to  produce  the  re- 
quired steam,  through  the  continual  opening  of  the  fire-doors  and 
the  raking  of  the  fires,  thus  cooling  the  combustion-chamber  and 
sifting  good  coal  into  the  ash-pit.  Ample  boiler  capacity  can  be 
secured  by  assuming  a  low  rate  of  combustion  in  proportion  to  the 
height  of  chimney,  but  a  low  rate  of  combustion  has  not  been  found 
economical,  and  much  must  depend  on  personal  experience. 


CHIMNEY-DRAFT  135 

Area  and  Height  of  Chimney.  —  The  area  and  height  of  chimney 
are  closely  allied,  since  the  product  of  area  times  velocity  measures 
the  quantity  of  gases  discharged,  and  the  velocity  is  dependent  upon 
the  height.  In  general,  the  shorter  the  chimney  the  larger  should 
be  the  area,  and  conversely. 

An  empirical  formula,  largely  used  by  engineers,  is  that  of 
William  Kent,  explained  in  Transactions  Am.  Soc.  M.  E.,  Vol.  VI, 
namely  : 

Let  E  denote  effective  area  of  chimney. 
"   A      "      actual  area  of  chimney. 
"  H      "      height  of  chimney. 

"  H.P."  the  horse-power,  based  on  a  coal  consumption  of 
5  pounds  of  coal  per  hour.  If  the  expected 
rate  of  coal  per  horse-power  be  different,  then 
the  result  must  be  corrected  by  multiplying  by 
the  ratio  of  5  to  the  maximum  expected  rate 
of  consumption  per  horse-power. 

Then 


_ 

VH 

This  formula  is  based  on  the  assumptions  that  the  draft  varies 
as  the  square  root  of  the  height,  that  the  retarding  of  the  ascending 
gases  by  friction  may  be  considered  as  equivalent  to  a  diminution  of 
the  area  of  chimney  equal  to  that  of  a  layer  2  inches  in  thickness, 
and  that  the  power  varies  directly  as  this  effective  area. 

Then,  for  round  flues,  diameter  =  diameter  of  E-\-4  inches; 
"  square   "      side         =  square  root  of  #+4  inches. 

The  Riter-Conley  Manufacturing  Company*  have  adopted  a 
formula  for  the  horse-power  of  chimneys  which  is  simpler  and 
appears  to  give  better  results  than  Kent's,  namely, 


*  Of  Pittsburg,  Pa.     Kindness  of  Mr.  Wm.  C.  Coffin,  Vice-President. 


136  STEAM-BOILERS 

in  which  H.P.  is  the  same  as  Kent's   definition,  D  the  internal 
diameter  in  feet,  and  H  the  height  above  grate  in  feet. 
John  W.  Hill  states  a  formula  as  follows: 

.1.8  grate  surface 

A.  —  —  —  ~.  —  —    —  . 

VH 

where  A  denotes  the  area  of  flue  and  //  the  height  above  the  grate. 
This  formula  is  based  on  experience  with  Western  bituminous 
coals  under  natural  draft,  and  burning  at  rates  varying  from  15 
to  25  pounds  per  square  foot  of  grate  per  hour. 

Prof.  A.  C.  Smith  states  a  formula  in  which  F  denotes  the  coal 
burned  per  hour  on  the  grate  in  pounds,  thus: 

A     0.0825F 

A    ~ 


„       0.0825/ 


Many  engineers  simply  adopt  the  following  proportions,  the  grate 
surface  being  taken  as  unity.  For  coals  midway  between  anthra- 
cite and  bituminous  use  intermediate  values.  For  rapid  rates  of 
combustion  use  proportionately  increased  values. 

Bituminous.         Anthracite. 

Area  over  bridge  wall  .............   V5  l/7 

Area  through  tubes,  or  calorimeter  .  .   V6  1/8 

Area  of  chimney-flue  ..............   l/7  V9 

It  is  well  to  proportion  an  ample  chimney  for  all  cases,  and  to 
use  the  damper  if  the  draft  be  too  strong.  There  is  then  a  reserve 
of  power  for  use  if  necessary. 

Chimneys  for  very  large  powers  need  not  have  so  great  an  area 
as  those  for  small  power,  in  proportion  to  their  size.  There  are 
cases,  with  large  batteries  of  boilers,  where  the  stack  has  worked 
well  when  the  flue-area  is  less  than  1/20  of  grate  surface. 

For  large  batteries  of  boilers  it  is  often  found  better  to  use  a 
number  of  smaller  chimneys  than  a  single  large  one,  as  so  much 
resistance  is  offered  by  the  long  connections  or  breechings,  as  to 


CHIMNEY-DRAFT  137 

require  the  single  chimney  to  be  extra  high.  Furthermore,  the 
boilers  nearest  the  chimney  will  rob  those  farther  away. 

As  very  high  chimneys  are  expensive  to  construct,  drafts  pro- 
duced by  mechanical  means  are  becoming  more  general,  and  can 
often  be  operated  and  maintained  for  the  interest  on  the  saving  of 
cost  of  stack.  Under  conditions  of  artificial  draft  the  areas  men- 
tioned just  above  should  be  increased  to  accommodate  the  greater 
quantity  of  fuel  burned. 

In  marine  practice  it  is  customary  to  increase  the  areas  above 
those  adopted  for  stationary  practice.  The  area  of  stack  is  often 
determined  by  the  general  appearance  of  the  vessel,  although  the 
modern  tendency  is  toward  high  funnels  with  somewhat  reduced 
diameters. 

For  equal  heights  the  draft  is  stronger  in  marine  boilers  than 
in  similar  ones  on  land,  so  that  the  area  in  any  event  should  be 
greater. 


CHAPTER  VII 
MATERIALS 

Cast  Iron.  Wrought  Iron.  Rivet-iron.  Charcoal-iron  for  Boiler-tubes. 
Wrought  Steel.  II.  S.  Naval  Requirements  for  Boiler-steel.  Steel  Rivets. 
Steel  for  Boiler-braces.  Mild  Steel  Affected  by  Temperature.  Cast  Steel. 
Copper.  Brass.  Bronze.  Muntz's  Metal. 

THE  materials  used  in  boiler-making  are  chiefly  cast  iron, 
wrought  iron,  steel,  cast  steel,  copper  and  brass. 

Cast  Iron  is  used  for  many  of  the  boiler  fittings,  supports  and 
accessories.  It  has  gradually  been  rejected  as  a  material  to  be 
worked  into  parts  subject  to  great  variation  of  heat  and  pressure, 
on  account  of  its  brittle  and  uncertain  nature  when  placed  under 
tensile  stress.  If  carefully  worked  and  finally  cast  only  after  re- 
peated remeltings,  so  as  to  render  it  homogeneous,  it  has  shown 
remarkable  properties  for  endurance,  even  under  severe  conditions. 
Owing  to  its  lack  of  tensile  strength,  parts  of  cast  iron  have  to  be 
made  very  thick,  and  are  thus  liable  to  internal  stresses  not  visible 
from  external  examination. 

Cast  iron  is  largely  used  for  furnace  and  ash-pit  doors  (although 
many  are  now  being  made  of  steel  and  cast  steel),  valve-casings, 
crosses  and  tees  for  boiler-mountings,  grate-bars  and  bearers,  man- 
hole and  handhole  covers,  supports,  supporting  lugs,  boiler-fronts, 
etc. 

Steam-pipes  are  occasionally  made  of  cast  iron,  but  this  practice 
is  not  to  be  recommended.  When  so  used  these  pipes  should  be 
carefully  drained,  so  as  to  prevent  any  water  collecting  in  them  from 
condensed  steam.  Such  water  must  be  blown  out  before  the  full 
steam-pressure  be  turned  on  the  piping. 

Many  of  the  more  important  pieces  are  best  made  of  malleable 
cast  iron;  and  this  material  is  largely  used  in  the  construction  of 
some  parts  of  water-tubular  boilers,  as  it  has  a  ductility  from  four 
to  six  times  greater  than  ordinary  cast  iron. 

138 


MATERIALS  139 

When  cast-iron  fittings  are  mounted  on  boilers,  use  care  not  to 
permit  water  to  lodge  in  them.  Many  boilers  have  been  exploded 
by  permitting  water  to  collect  on  top  of  cast-iron  stop-valves. 
This  can  be  best  prevented  by  designing  a  proper  placing  of  the  valve 
or  mounting  so  as  to  be  self-draining,  or  by  fitting  a  drain-pipe  which 
must  be  opened  first. 

The  cast  irons  are  frequently  known  by  numbers ;  thus  number 
one  contains  the  most  graphite  or  carbon,  while  the  higher  numbers 
the  least.  The  numbers  run  from  one  to  seven.  They  are  fre- 
quently known  by  names  of  the  districts  in  which  made.  The 
commonest  designation  divides  the  irons  into  three  classes,  thus: 
number  one,  gray  iron  or  foundry  iron;  number  two,  mottled  iron; 
and  number  three,  white  iron.  The  numbers  two  and  three  are 
sometimes  called  " forge"  irons. 

The  best  irons  for  strong  castings  are  made  from  mixtures,  thus 
combining  desired  qualities  as  strength,  fluidity,  close-grained,  etc. 

Hardness  can  be  obtained  by  mixing  steel  scrap,  which  will  give 
a  close-grained  and  strong  casting.  The  scrap  may  be  added  in 
amounts  as  much  as  10  to  15  per  cent.  Little  is  gained  by  increasing 
the  amount  of  scrap,  as  the  iron  becomes  so  hard  as  to  be  available 
only  for  thick  castings  without  complications  of  form. 

The  strongest  cast  irons  are  of  a  light-gray  color,  and  on  fracture 
should  exhibit  a  close,  uniform  grain.  The  tensile  strength  should 
not  be  less  than  18,000  pounds,  and  the  crushing  strength  110,000 
pounds  per  square  inch.  For  all  important  work  the  iron  should 
be  made  from  selected  scrap,  or  should  be  remelted  at  least  once. 
Remelting  improves  the  quality  until  the  process  has  been  repeated 
about  twelve  times. 

Wrought  Iron  is  now  little  used,  having  yielded  its  place  to 
wrought  steel.  The  chief  objection  to  wrought  iron  is  its  lack  of 
uniformity  or  homogeneity,  due  to  the  existence  of  blisters  and 
laminations,  often  difficult  to  detect  from  surface  examination. 
These  defects  can  usually  be  detected  by  tapping  the  sheet  with  a 
light  hammer,  especially  when  the  sheet  is  supported  on  two 
diagonally  opposite  corners. 

Many  engineers  prefer  wrought  iron  to  steel  plates  for  tank  and 
other  cheap  work,  since  the  poorest  grades  of  the  latter  are  likely  to 
IDC  used,  and  such  steel  will  not  stand  the  same  amount  of  rough 
usage  in  handling  and  bending  as  the  iron. 


140  STEAM-BOILERS 

Wrought  iron  is  never  obtained  commercially  pure,  but  is 
always  mixed  with  more  or  less  slag,  and  such  elements  as  carbon, 
sulphur,  phosphorus,  silicon  and  manganese. 

The  usual  proportion  of  these  elements  should  not  exceed  the 
following  amounts,  expressed  in  percentage : 

From  To 

Carbon 0.020  0.20 

Sulphur 0.000  0.01 

Phosphorus 0.050  0.25 

Silicon 0.050  0.30 

Manganese 0.005  0.05 

Sulphur  in  excess  of  the  above  quantity  makes  the  iron  brittle 
when  heated  to  redness,  or  red-short;  phosphorus,  brittle  when  cold, 
or  cold-short.  The  effect  of  silicon  and  manganese  appears  to  be 
important. 

Good  iron  boiler-plate  should  show  a  tensile  strength  of  from 
48,000  to*  56,000  pounds  per  square  inch,  an  elongation  of  not  less 
than  10  or  15  per  cent  in  test  pieces  8  inches  between  marks,  and  a 
reduction  of  area  of  not  less  than  40  per  cent.  The  elastic  limit  is 
about  27,000  pounds. 

The  appearance  of  the  fracture  depends  on  the  manner  in  which 
the  specimen  was  broken.  When  the  pressure  is  applied  slowly, 
good  wrought  iron  should  exhibit  a  fibrous  and  irregular  fracture, 
while  a  poorer  quality  will  show  a  more  regular  fracture,  the  fibres 
being  broken  across  and  mixed  with  crystalline  structure.  The  fine- 
ness and  coarseness  may  be  taken  as  a  test  of  quality.  On  the 
other  hand,  when  suddenly  torn  apart  or  broken  by  a  sharp  trans- 
verse blow,  good  iron  will  show  a  fine  crystalline  fracture,  while 
the  poorer  qualities  exhibit  a  much  coarser  structure.  The  fibrous 
nature  may  all  be  lost  by  the  sudden  action  of  the  fracture. 
Wrought  iron  should  never  be  judged  as  to  quality,  unless  the 
method  of  making  the  fracture  be  positively  known. 

Wrought  iron  is  preferred  by  many  for  rivets,  although  recent 
improvements  in  steel  manufacture  have  been  instrumental  in 
introducing  the  latter  in  preference  to  iron,  especially  for  heavy 
work.  As  iron  is  less  apt  to  be  injured  by  working  cold  and  also  by 
being  overheated  in  the  forge,  iron  rivets  should  be  used  when 
driven  cold  or  for  use  in  cheap  work. 


MATERIALS  141 

Rivet-iron  should  be  soft  and  of  the  best  quality,  as  it  has  to 
withstand  hard  usage.  The  tensile  strength  should  be  not  less 
than  50,000  pounds  per  square  inch,  and  its  resistance  to  shearing  is 
usually  from  38,000  to  40,000  pounds  per  square  inch.  A  rivet 
should  bend  double  when  cold,  without  fracture;  and  when  hot,  the 
head  should  be  capable  of  being  flattened  to  about  J  inch  in  thick- 
ness without  fraying  at  the  edge.  The  minimum  elongation  in 
specimens  8  inches  long  should  be  not  less  than  18  per  cent,  and  the 
minimum  contraction  should  be  not  less  than  40  per  cent.  When 
the  bar  is  bent  after  having  been  nicked  on  one  side,  the  fracture 
should  be  fibrous. 

Tests  should  not  be  made  on  bars  less  than  8  inches  long  between 
marks,  nor  of  less  sectional  area  than  ^  square  inch. 

Stays  and  all  pieces  that  have  to  be  forged  or  welded  are  best 
made  of  iron,  of  the  same  quality  as  for  rivets. 

Wrought  iron  is  used  for  making  boiler-tubes,  although  many 
are  made  of  steel.  Charcoal-iron  is  considered  the  best  grade  for 
tubes.  It  is  very  difficult  to  detect  the  difference  between  charcoal- 
iron  and  steel  tubes  by  surface  inspection,  but  the  material  can  be 
readily  identified  from  the  fracture. 

Wrought  iron  for  tubes  should  have  a  tensile  strength  of  not 
less  than  49,000  pounds  and  an  elongation  of  at  least  15  per  cent  in 
a  length  of  8  inches. 

The  requirements  of  the  Bureau  of  Steam  Engineering,  U.  S. 
Navy  Department,  1897,  for  charcoal-iron  boiler-tubes  are  as 
follows : 

SPECIFICATIONS  FOR  CHARCOAL-IRON  BOILER-TUBES. 

1.  The  tubes  must  be  made  of  the  best  quality  of  knobbled,  ham- 
mered charcoal-iron,  and  tests  will  be  made  both  of  the  skelp  and  of  the 
finished  tubes  to  determine  whether  or  not  such  material  has  been  used. 
Pig  iron  only  will  be  used  in  the  manufacture  of  the  blooms.     The  tubes 
must  be  of  uniform  gauge  throughout,  and  be  smooth  and  free  from  rust, 
scale,  pits,  laminations,  or  imperfect  welds. 

2.  Strips  one-half  inch  in  width  will  be  cut  lengthwise  from  the  tubes; 
these  strips  will  be  heated  to  a  bright  cherry-red,  in  daylight,  and  plunged 
(while  at  this  heat)  in  water  at  a  temperature  of  80°  F. ;   after  being  so 
quenched  a  strip  must  bend,  cold,  back  upon  itself  without  crack  or 
flaw.     Strips  so  heated  and  quenched  must  not  show  lamination  when 
hammered. 


142  STEAM-BOILERS 

3.  The  end  of  a  tube  will  be  heated  to  a  bright  cherry-red,  in  day- 
light, for  a  distance  equal  to  one  and  one-half  (1^)  times  its  diameter, 
and  a  taper-pin,  at  a  blue  or  dull-red  heat,  driven  in.     The  tube  must 
stretch  to  one  and  one-eighth  (1£)  times  its  original  diameter  without 
split  or  crack.     The  taper  of  the  pin  must  not  exceed  one  in  eight  (1^ 
inches  to  the  foot),  and  its  surface  must  be  smooth. 

4.  Each  tube  will  be  subjected  to  an  internal  hydrostatic  pressure  of 
500  pounds  to  the  square  inch. 

5.  These  tests  will  be  made  by  an  engineer  officer,  and  one  tube  will 
be  selected  by  him,  personally,  for  test  from  each  lot  of  250  or  fraction 
thereof,  unless  in  his  opinion  a  larger  number  must  be  tested  to  enable 
him  to  form  a  proper  estimate  of  the  quality  of  the  whole  lot.     The  sur- 
face inspection  will,  of  course,  be  made  on  each  tube  of  the  whole  lot. 

6.  Failure  to  pass  satisfactorily  any  of  the  above  tests  will  be  cause 
for  rejection  of  the  whole  lot  of  tubes. 

Steel.  The  material  almost  exclusively  used  for  boiler  con- 
struction at  the  present  time  is  mild  steel,  since  it  is  stronger,  has 
a  higher  elastic  limit,  greater  elasticity,  and  is  more  homogeneous 
in  structure  than  wrought  iron. 

Steel  may  be  considered  as  an  alloy  of  iron,  and  can  be  placed 
midway  between  the  cast  and  wrought  irons. 

Only  the  milder  steels,  those  containing  low  percentages  of 
carbon,  are  used  for  boiler- work  in  order  to  take  advantage  of  the 
greater  homogeneity  and  higher  ductility. 

The  best  boiler-steel  plates  are  made  by  the  Siemens-Martin 
or  open-hearth  process,  although  many  of  the  cheaper  boilers  are 
made  of  Bessemer  plates. 

Steel  is  liable  to  injury  while  working,  and  all  pieces  that  have 
been  subjected  to  a  partial  heat,  as  in  flanging,  should  be  annealed 
to  restore  the  original  toughness.  Steel  is  liable  to  become  brittle 
when  worked  cold.  The  act  of  punching  for  rivet-holes  injures  steel 
plates,  especially  if  they  are  hard.  Steel  plates  should  always  be 
drilled,  or  if  punched,  the  holes  should  be  reamed  out  to  remove  the 
injured  material. 

Steel  is  used  for  rivets  and  tubes,  and  good  results  are  obtained 
if  care  is  taken  in  the  selection  of  the  material. 

The  tensile  strength  is  usually  limited  between  60,000  and  73,000 
pounds  per  square  inch.  If  the  limits  are  placed  close,  the  cost 
rapidly  increases.  The  object  of  having  a  maximum  as  well  as  a 
minimum  limit  is  to  give  uniformity  to  all  parts  alike,  since  the 


MATERIALS  143 

steel  becomes  hard  and  loses  ductility  and  elasticity  as  the  strength 
increases.  For  all  flanged  pieces  the  tensile  strength  is  generally 
limited  between  52,000  and  60,000  pounds. 

For  ordinary  commercial  work  the  elongation  in  specimens  8 
inches  long  should  be  at  least  20  per  cent  for  shells,  25  per  cent  for 
flanged  pieces,  and  27  per  cent  for  stays;  and  the  contraction  of 
area,  50  per  cent  for  plates  J  inch  thick  and  less,  45  per  cent  for  J  to 
f  inch,  and  40  per  cent  for  all  over  }  inch. 

All  the  boiler  accessories  not  directly  contributing  to  strength, 
such  as  fire-doors,  ash-pit  doors,  smoke-pipes,  etc.,  may  be  made  of 
a  poorer  grade  of  steel. 

The  requirements  of  the  U.  S.  Navy  Department,  1899,  are  as 
below : 

SPECIFICATIONS  FOR  BOILER-PLATE  AND  SHAPES. 
BOILER-PLATE.     (CLASS  A.) 

Kind  of  Material. — Steel  for  boiler-plates  shall  be  made  by  the  open- 
hearth  process,  and  not  show  more  than  thirty-five  one-thousandths  of 
1  per  cent  of  phosphorus  nor  more  than  three  one-hundredths  of  1  per 
cent  of  sulphur,  and  be  of  the  best  composition  in  other  respects. 

Test  Specimens. — One  tensile-test  piece,  taken  longitudinally,  and 
one  bending-test  piece,  taken  transversely,  shall  be  cut  from  each  plate 
as  rolled  for  boilers,  as  directed  by  the  Naval  Inspector.  The  cold-bend- 
ing pieces  must  not  have  their  sheared  nor  planed  sides  rounded  off,  but 
the  sharpness  of  the  edges  may  be  taken  off  with  a  fine  file. 

Tensile  Tests  of  Class  A  No.  1  Plates. — Test  specimens  must  show  a 
tensile  strength  of  at  least  74,000  pounds  per  square  inch,  with  an  elastic 
limit  of  40,000  pounds  per  square  inch,  and  an  elongation  of  at  least  21 
per  cent  in  eight  (8)  inches. 

Tensile  Tests  of  Class  A  No.  2  Plates. — Test  specimens  must  show  a 
tensile  strength  of  at  least  66,000  pounds  per  square  inch,  with  an  elastic 
limit  of  at  least  36,000  pounds  per  square  inch,  and  an  elongation  of  at 
least  23  per  cent  in  eight  (8)  inches. 

Tensile  Tests  of  Class  A  No.  3  Plates. — Test  specimens  must  show  a 
tensile  strength  of  at  least  60,000  pounds  per  square  inch,  with  an  elastic 
limit  of  at  least  32,000  pounds  per  square  inch,  and  an  elongation  of  at 
least  25  per  cent  in  eight  (8)  inches. 

Cold-bending  Test. — One  specimen  cut  from  each  Class  A  No.  1  and 
Class  A  No.  2  plate,  as  finished  at  the  rolls  for  cold-bending  test,  shall 
bend  round  a  curve  the  diameter  of  which  is  equal  to  the  thickness  of 
the  plate  tested  till  the  sides  of  the  specimen  are  parallel,  without  signs 
of  fracture  on  the  outside  of  the  bent  portion. 


144  STEAM-BOILERS 

Cold-bending  Test. — One  specimen  cut  from  each  Class  A  No.  3  plate 
shall  bend  flat  on  itself  without  signs  of  fracture  on  the  outside  of  the 
bent  portion. 

Inspection  for  Surface  and  Other  Defects. — Plates  must  be  free  from 
slag,  foreign  substances,  brittleness,  laminations,  hard  spots,  injurious 
sand  or  scale  marks,  scabs,  snakes,  and  injurious  defects  generally. 

Shearing. — Boiler-plates  thirteen-sixteenths  (rt)  of  an  inch  thick  and 
over  shall  not  be  sheared  closer  to  finished  dimensions  than  once  the 
thickness  of  the  plate  along  each  end,  and  one  half  the  thickness  of  the 
plate  along  each  side.  This  allowance  shall  be  made  by  the  contractor 
on  his  order,  and  the  manufacturer  shall  shear  to  ordered  dimensions. 

Weight  and  Gauge. — Contractors  shall  enter  on  their  orders  to  manu- 
facturers both  weight  per  square  foot  and  gauge  of  plates.  Plates  shall 
not  vary  from  the  specified  weight  more  than  the  following  amounts: 
2  per  cent  below  and  7  per  cent  above  for  plates  more  than  one  hun- 
dred and  ten  (110)  inches  wide;  2  per  cent  below  and  6  per  cent  above 
for  plates  between  one  hundred  (100)  and  one  hundred  and  ten  (110) 
inches  wide;  2  per  cent  below  and  5  per  cent  above  for  plates  between 
eighty  (80)  and  one  hundred  (100)  inches  wide;  2  per  cent  below  and  4 
per  cent  above  for  plates  between  sixty  (60)  and  eighty  (80)  inches  wide; 
and  2  per  cent  below  and  3  per  cent  above  for  plates  less  than  sixty  (60) 
inches  wide. 

Gauge. — No  plate  must,  at  any  point,  fall  below  the  specified  thick- 
ness more  than  the  following  amounts:  Six  one-hundredths  (T{jtf)  of  an 
inch  for  plates  more  than  one  hundred  and  ten  (110)  inches  wide;  five 
one-hundredths  (TTTS)  of  an  inch  for  plates  between  one  hundred  (100) 
and  one  hundred  and  ten  (110)  inches  wide;  four  one-hundredths  (Tfa) 
of  an  inch  for  plates  between  eighty  (80)  and  one  hundred  (100)  inches 
wide;  three  one-hundredths  (T§zO  of  an  inch  for  plates  between  sixty  (60) 
and  eighty  (80)  inches  wide;  and  two  one-hundredths  (^)  of  an  inch 
for  plates  less  than  sixty  (60)  inches  wide. 

Oil-tempering  and  Annealing. — It  is  left  optional  with  the  manufac- 
turers to  oil-temper  and  anneal  Class  A  No.  1  plates  of  a  thickness  greater 
than  one  (1)  inch,  in  order  to  get  the  requirements  of  these  specifications; 
but  the  oil-tempering  and  annealing  must  be  done  before  the  plate  is 
submitted  to  the  Naval  Inspector  for  tests. 

SPECIFICATIONS  FOR  RODS,  SHAPES,  AND  FORCINGS  FOR 
BOILER  BRACING. 

BOILER  BRACING.     (CLASS  A.) 

Kind  of  Material — Steel  for  stay-bolts  and  braces  shall  be  made 
by  the  open-hearth  process,  shall  not  show  more  than  thirty-five  one- 


MATERIALS  145 

thousandths  of  1  per  cent  of  phosphorus,  nor  more  than  three  one- 
hundredths  of  1  per  cent  of  sulphur,  and  shall  be  of  the  best  compo- 
sition in  other  respects.  The  drillings  for  chemical  analysis  shall  be 
taken  from  the  same  objects  as  the  tensile-test  pieces. 

One  ton  of  material  for  boiler  braces,  from  the  same  heat,  shall 
constitute  a  lot  from  which  two  tensile  and  one  cold-bending  test  speci- 
mens shall  be  taken,  each  from  a  different  object. 

Treatment. — All   material   for  boiler  bracing   shall    be  annealed  as  a 
final  process. 

Tensile  Tests  of  Class  A  No.  1  Bracing. -^Test  specimens  must  show 
a  tensile  strength  of  at  least  74,000  pounds  per  square  inch,  with  an 
elastic  limit  of  at  least  40,000  pounds  per  square  inch,  and  an  elonga- 
tion of  at  least  22  per  cent  in  eight  (8)  inches,  or  26  per  cent  in  two  (2) 
inches,  in  case  8-inch  specimens  cannot  be  secured. 

Tensile  Tests  of  Class  A  No.  2  Bracing. — Test  specimens  must  show 
a  tensile  strength  of  at  least  66,000  pounds  per  square  inch,  with  an 
elastic  limit  of  at  least  36,000  pounds  per  square  inch,  and  an  elonga- 
tion of  at  least  24  per  cent  in  eight  (8)  inches,  or  28  per  cent  in  two  (2) 
inches,  in  case  8-inch  specimens  cannot  be  secured. 

Tensile  Tests  of  Class  A  No.  3  Bracing. — Test  specimens  must  show 
a  tensile  strength  of  at  least  60,000  pounds  per  square  inch,  with  an 
elastic  limit  of  at  least  32,000  pounds  per  square  inch,  and  an  elonga- 
tion of  at  least  26  per  cent  in  eight  (8)  inches,  or  30  per  cent  in  two  (2) 
inches,  in  case  8-inch  specimens  cannot  be  secured. 

Cold-bending  Test. — One  bar,  one-half  (£)  inch  thick,  cut  from  each 
lot  of  Class  A  No.  1  bracing  shall  stand  cold-bending  double  to  an  inner 
diameter  of  one  (1)  inch,  the  ends  of  the  piece  being  brought  parallel, 
without  showing  signs  of  fracture  on  the  outside  of  the  bent  portion. 

Cold-bending  Test. — One  bar,  one-half  (£)  inch  thick,  cut  from  each  lot 
of  Class  A  No.  2  bracing  shall  stand  cold-bending  double  to  an  inner 
diameter  of  one-half  (£)  inch,  the  ends  of  the  piece  being  brought  par- 
allel, without  showing  signs  of  fracture  on  the  outside  of  the  bent  portion. 

Cold-bending  Test. — One  bar,  one-half  (£)  inch  thick,  cut  from  each 
lot  of  Class  A  No.  3  bracing  shall  stand  cold-bending  flat  on  itself,  the 
•ends  of  the  piece  being  brought  parallel,  without  showing  signs  of  frac^- 
ture  on  the  outside  of  the  bent  portion. 

Opening  and  Closing  Tests. — Angles,  T  bars,  and  other  shapes  are 
to  be  subjected  to  the  following  additional  tests:  A  piece  cut  from  one 
bar  in  twenty  shall  be  opened  out  flat  while  cold,  without  showing 
cracks  or  flaws;  a  piece  cut  from  another  bar  in  the  same  lot  shall  be 
closed  down  on  itself  until  the  two  sides  touch,  without  showing  cracks 
or  flaws. 

Inspection  for  Surface  and  other  Defects. — Stay-rods  and  bracing  must 


14t>  STEAM-BOILERS 

be  true  to  form,  free  from  seams,  hard  spots,  brittleness,  injurious  sand 
or  scale  marks,  and  injurious  defects  generally. 

Boiler-plate  used  as  boiler  bracing  shall  be  inspected  as  plate  under 
the  specifications  for  boiler-plate  of  the  class  required  by  the  Machinery 
Specifications. 

SPECIFICATIONS  FOR  RIVET-RODS  AND  FINISHED  RIVETS. 

Kind  of  Material. — High-grade  and  Class  A  material  shall  be  made 
by  the  open-hearth  process,  shall  not  show  more  than  thirty-five  one- 
thousandths  of  1  per  cent  of  phosphorus  nor  more  than  three  one- 
hundredth  s  of  1  per  cent  of  sulphur,  and  shall  be  of  the  best  composi- 
tion in  other  respects. 

Class  B  material  rnay  be  made  by  the  open-hearth  or  Bessemer 
process,  as  ordered.  The  material  shall  not  show  more  than  nine  one- 
hundredths  of  1  per  cent  of  phosphorus,  nor  more  than  six  one-hun- 
dredths  of  1  per  ce*nt  of  sulphur,  and  may  be  used  on  work  specified 
as  Class  B,  and  in  other  work,  if  permitted  by  the  Machinery  Specifica- 
tions. 

The  drillings  for  chemical  analysis  shall  be  taken  from  the  cold- 
bending  test  specimens. 

TENSILE,   COLD-BENDING,    AND    QUENCHING   TESTS. 

Test  Specimens. — If  the  total  weight  of  rods  rolled  from  a  heat 
amounts  to  more  than  six  tons,  then  the  Naval  Inspector  shall  select, 
at  random,  six  tensile-test  pieces,  three  cold-bending-test  pieces,  and 
three  quenching-test  pieces.  If  the  total  weight  of  rods  rolled  from 
a  heat  amounts  to  less  than  six  tons,  then  the  Xaval  Inspector  shall 
select,  at  random,  one  tensile,  one  cold-bending,  and  one  quenching 
test  piece  for  each  ton  or  part  of  ton. 

Tensile,  cold-bending,  and  quenching  test  specimens  shall  be  cut 
from  rods,  finished  in  the  rolls,  and  only  one  specimen  is  to  be  cut  from 
each  rod  selected  for  test. 

Should  the  specimen  cut  be  so  large  in  cross-section  that  its  ultimate 
strength  exceeds  the  capacity  of  the  testing-machine,  then  the  specimen 
is  to  be  machined  to  the  largest  cross-section  which  can  be  broken  in 
the  testing-machine.  If  only  one  of  these  rods  selected  for  test  fails,  the 
Naval  Inspector  shall. select  another  rod  from  the  same  lot  and  put  it 
through  the  same  test  as  the  one  that  failed,  and  if  it  is  found  satisfac- 
tory he  shall  pass  the  lot.  The  tensile  test  of  sizes  of  rounds  under 
five-eighths  (f )  of  an  inch  in  diameter  shall  be  made  on  rounds  of  five- 
eighths  (|)  of  an  inch  in  diameter. 

High-grade  rivet-rods,  of  nickel  steel,  shall  have  at  least  75,000  pounds 


MATERIALS  147 

per  square  inch  tensile  strength,  with  an  elastic  limit  of  at  least  40,000 
pounds  per  square  inch,  and  an  elongation  of  at  least  23  per  cent  in 
eight  (8)  inches. 

Class  A  rivet-rods,  of  open-hearth  steel,  shall  have  at  least  60,000 
pounds  per  square  inch  tensile  strength,  with  an  elastic  limit  of  at  least 
32,000  pounds  per  square  inch,  and  an  elongation  of  at  least  26  per  cent 
in  eight  (8)  inches. 

Class  B  rivet-rods,  of  open-hearth  or  Bessemer  steel,  shall  have  at 
least  54,000  pounds  per  square  inch  tensile  strength,  with  an  elastic 
limit  of  at  least  30,000  pounds  per  square  inch,  and  an  elongation  of  at 
least  29  per  cent  in  eight  (8)  inches. 

Cold-bending  Test. — High-grade  rods  shall  stand  cold-bending  180 
degrees  to  an  inner  diameter  equal  to  the  thickness  or  diameter  of  the 
specimen. 

Class  A  rods  shall  stand  cold-bending  180  degrees  to  an  inner  diam- 
eter equal  to  one-half  the  thickness  or  diameter  of  the  specimen. 

Class  B  rods  shall  stand  cold-bending  180  degrees,  face  to  face. 

All  cold-bending  tests  will  be  satisfactory  if  the  specimens  show  no 
cracks  on  the  outside  of  the  bend. 

Quenching  Test. — The  specimen  shall,  after  heating  to  a  dark  cherry- 
red,  in  daylight,  be  plunged  into  water  of  a  temperature  of  82°  F.,  and 
shall  then  stand  bending  double  to  an  inner  diameter  of  one-half  inch 
without  showing  cracks  or  flaws  on  the  outside  of  the  bent  portion. 

HAMMER  TESTS   ON   FINISHED    RIVETS.     ' 

Hammer  Tests.— For  each  ton  or  less  of  finished  rivets,  made  from 
the  same  heat,  four  rivets  shall  be  selected,  at  random,  by  the  Naval 
Inspector  and  submitted  to  the  following  tests: 

(a)  Two  of  these  specimens  to  be  flattened  out  cold  to  a  thickness 
of  one-half  the  original  diameter  or  thickness  of  the  part  flattened  with- 
out showing  cracks. 

(6)  Two  of  these  specimens  to  be  flattened  out  hot  to  a  thickness 
of  one-third  of  the  original  diameter  or  thickness  of  the  part  flattened 
•without  showing  cracks,  the  heat  to  be  a  cherry-red  in  daylight. 

SURFACE    INSPECTION. 

Rivets  shall  be  true  to  form,  concentric,  and  free  from  injurious 
scale,  fins,  seams,  and  all  other  injurious  defects. 

Some  very  interesting  experiments  were  made  in  1898  by 
Maunsel  White  at  the  Bethlehem  Iron  Co.  on  the  use  of  nickel-steel 


148  STEAM-BOILERS 

for  rivets.*  The  results  showed  that  such  steel  could  be  subjected 
to  the  working  heats  without  serious  injury,  and  that  a  f-inch 
nickel-steel  rivet  was  about  equal  to  a  l^g-inch  common  steel  rivet, 
thus  saving  a  considerable  portion  of  plate  section.  This  material 
may  replace  ordinary  steel  for  many  uses. 

Nickel-steel  contains  about  0.23%  carbon,  0.02%  sulphur,  0.55% 
manganese,  3.50%  nickel,  0.02%  phosphorus.  The  ultimate 
strength  is  about  84,000  pounds  per  square  inch,  the  elastic  limit 
about  52,000  to  55,000  pounds,  the  elongation  about  20%,  and 
reduction  of  area  about  50%  to  60%.  The  shearing  strength  is 
about  equal  to  the  tensile  strength.  The  shearing  strength  of 
common  steel  rivets  is  about  43,000  to  46,000  pounds  per  square 
inch. 

The  tensile  strength  of  mild  steel,  such  as  used  for  boiler-plates 
and  furnaces,  is  appreciably  affected  by  temperature.  The  results 
of  experiments  made  by  the  United  States  Navy  Department, 
1888,  as  briefly  stated  by  D.  B.  Morison  (see  Gassier 's  Magazine, 
August,  1897)  were  as  below: 

"The  tensile  strength  of  all  steel  varies  between  zero  and  200 
degrees  Fahr. ;  the  maximum  strength  is  between  400  degrees  and 
600  degrees,  and  beyond  600  degrees  the  tensile  strength  decreases 
rapidly.  Although  the  ultimate  tensile  strength  increases  from 
200  to  600  degrees,  the  elastic  limit  steadily  decreases  from  zero 
upwards,  and  steel,  having  an  elastic  limit  of  35,000  pounds  per 
square  inch  at  zero,  has  its  elastic  limit  reduced  to  20,000  pounds 
per  square  inch  at  600  degrees  Fahr." 

"Another  point  is  that  the  higher  carbon  steels  reach  a  tempera- 
ture of  maximum  strength  more  abruptly  and  retain  their  highest 
strength  over  a  less  range  of  temperature  than  steels  having  a  low 
percentage  of  carbon." 

"In  furnaces  from  \  inch  to  f  inch  thick,  under  200  pounds 
steam-pressure,  the  temperature  of  the  plate,  when  clean,  ap- 
proaches a  temperature  of  maximum  tensile  strength;  therefore 
the  use  of  hard,  brittle  steel  is  rendered  dangerous,  especially  with 
furnaces  of  very  rigid  design." 

Cast  Steel.  The  quality  and  reliability  of  cast  steel  has  been 
so  advanced  in  the  past  few  years  as  to  render  the  material  very 

*  See  Journal  Am.  Soc.  Naval  Engineers,  November,  1898. 


MATERIALS  149 

popular  for  use  in  odd  shapes,  which  were  formerly  made  of  wrought- 
iron  forgings.  The  danger  of  flaws  is  fast  disappearing,  and  so 
great  a  confidence  is  being  placed  in  cast  steel  that  it  is  super- 
seding cast  iron  for  many  uses.  As  the  demand  increases,  no  doubt 
its  manufacture  will  be  vastly  improved. 

It  is  used  for  many  fittings  for  water-tube  boilers,  manhole  and 
handhole  covers,  ends  for  small  steam-  and  mud-drums,  grate-bars, 
etc. 

Castings  always  should  be  designed  with  as  even  a  thickness  as 
possible  throughout,  and  all  sharp  angles  be  rigidly  avoided  by 
using  large  fillets.  If  care  in  this  particular  be  not  taken,  the  cast- 
ing is  apt  to  be  weak  or  defective  from  internal  shrinkage  stresses, 
and  liable  to  crack. 

As  defects,  blow-holes,  etc.,  in  steel  castings  are  usually  near  the 
surface  uppermost  in  the  cast  or  at  the  centre  of  the  upper  end,  care 
must  be  taken  in  making  the  mould,  so  that  the  defects  can  be  most 
readily  seen  or  be  machined  out  while  the  piece  is  being  shop- 
finished. 

The  tensile  strength  of  cast  steel  is  very  high,  but  rapidly  loses 
in  elasticity.  It  is  most  difficult  to  keep  the  strength  low  and  thus 
obtain  a  high  elasticity.  Cast  steel  with  a  tensile  strength  of 
58,000  to  60,000  pounds  should  have  an  elongation  of  from  10  to  15 
per  cent  in  8-inch  test  pieces.  When  the  strength  is  between 
60,000  and  70,000  pounds  the  elongation  should  never  be  less  than 
10  per  cent,  and  may  be  as  high  as  18  per  cent.  For  all  important 
pieces  the  casting  should  be  annealed  to  reduce  the  tensile  strength 
and  increase  the  elongation. 

Cast-steel  specimens  of  round  or  square  section,  1^  inches  thick 
and  less,  should  be  capable  of  bending  cold  without  fracture  through 
an  angle  of  90  degrees,  over  an  inner  radius  not  exceeding  If  inches, 
when  tensile  strength  is  60,000  pounds;  and  through  an  angle  10 
degrees  less  for  each  increase  of  5000  pounds  in  tensile  strength. 

Defects  should  not  be  made  good  by  patching  or  by  electric 
welding,  unless  done  under  careful  supervision. 

The  requirements  of  the  U.  S.  Navy  Department,  1899,  are  in 
abstract  as  below: 

Sound  test  pieces  shall  be  taken  in  sufficient  number  to  exhibit  the 
character  of  the  metal  in  the  entire  piece. 

A  lot  shall  consist  of  all  castings  from  the  heat  annealed  in  the  same 


150  STEAM-BOILERS 

furnace  charge.  From  each  lot  two  tensile  and  one  bending  specimen 
shall  be  taken. 

If  there  are  any  unsound  test  specimens  coming  from  a  casting, 
the  inspector  shall  examine  carefully  to  detect  porosity  or  other  un- 
soundness  in  the  casting  itself. 

Steel  for  castings  shall  be  made  by  either  open-hearth  or  crucible 
process,  and  no  casting  shall  show  more  than  six  one-hundredths  (0.06) 
of  one  per  cent  of  phosphorus  and  shall  be  of  the  best  composition  in 
other  respects.  All  castings  shall  be  annealed  unless  otherwise  ordered. 

The  tensile  strength  of  castings  shall  be  at  least  60,000  pounds  per 
square  inch,  with  an  elongation  of  at  least  15  per  cent  in  eight  inches 
for  all  castings  for  moving  parts  of  machinery,  and  at  least  10  per  cent 
for  all  other  castings.  In  thin  castings,  the  inspector  may  require 
specimens  two  inches  in  length  to  show  20  per  cent  elongation  with 
62,000  pounds  tensile  for  moving  parts,  and  15  per  cent  elongation  with 
60,000  pounds  tensile  for  other  parts. 

A  test  to  destruction  may  be  substituted  for  the  tensile  test,  in  the 
case  of  small  and  unimportant  castings.  This  test  must  show  the 
material  to  be  ductile  and  free  from  injurious  defects  and  suitable  for 
the  purposes  intended. 

One  bar  or  more  from  each  important  casting  or  one  bar  from  each 
.lot,  one  inch  square,  shall  be  bent  cold  without  showing  cracks  or  flaws, 
through  an  angle  of  120  degrees  for  castings  for  moving  parts  of  machin- 
ery, and  90  degrees  for  other  castings,  over  a  radius  not  greater  than 
one  and  one-half  inches.  In  cases  where  two-inch  tensile  specimens 
are  used,  a  bending  specimen  one  inch  by  one-half  inch  shall  be  bent 
cold  through  150  degrees  without  showing  cracks  or  flaws,  for  castings 
for  moving  parts  of  machinery,  and  120  degrees  for  other  castings. 

All  castings  must  be  sound,  free  from  brittleness,  injurious  rough- 
ness, sponginess,  pitting,  porosity,  shrinkage  and  other  cracks,  cavities, 
foreign  or  other  substances,  and  all  other  defects  affecting  their  value. 
Particular  search  must  be  made  at  the  points  where  the  heads  or  risers 
join  the  castings,  as  unsoundness  at  this  point  is  likely  to  extend  into 
the  castings. 

Copper.  The  use  of  copper  in  boiler  construction  has  gradually 
decreased,  except  for  certain  adjuncts,  as  steam-pipes,  feed  and 
blow-off  pipes,  gaskets,  etc.  It  is  still  used  to  a  limited  extent  for 
fire-box  sheets  in  boilers  of  the  locomotive  type. 

It  is  very  ductile,  and  can  be  joined  by  brazing  so  as  to  be  as 
strong  as  the  original  piece.  The  greatest  care  must  be  taken  not 
to  burn  the  copper  while  being  prepared  for  brazing. 


MATERIALS  151 

It  does  not  corrode  under  the  action  of  air  or  water,  either  fresh 
or  salt,  although  certain  waters  containing  free  gases  appear  to  act 
deleteriously  upon  it.  It  is  extremely  useful  for  forming  alloys, 
as  it  is  much  improved  by  small  quantities  of  other  metals.  It  is 
expensive,  has  a  low  tensile  strength  and  weakness  to  resist  abrasion. 

The  more  copper  is  worked  the  stronger  it  becomes  within 
reasonable  limits.  Its  strength  depends  upon  its  quality.  Cast 
copper  has  a  tensile  strength  of  about  22,000  pounds,  forged 
copper  about  31,000  pounds  and  rolled  copper  about  33,000 
pounds.  Copper  wire  has  a  strength  of  about  60,000  pounds  before 
annealing  and  40,000  pounds  after  annealing. 

For  all  calculations  sheet  copper  can  be  figured  at  30,000  pounds 
in  default  of  full  information.  At  high  temperatures  copper  rapidly 
loses  strength,  becomes  plastic  at  about  1330  degrees  and  melts 
at  about  2000  degrees  Fahrenheit. 

Copper  may  be  solid-drawn  into  pipes  as  large  as  8  inches 
diameter. 

From  a  paper  by  J.  T.  Milton  read  at  the  14th  Session  of 
the  Institution  of  Naval  Architects,  London,  1899,  the  following 
paragraphs  are  extracted: 

"  Hardening  of  copper  may  be  produced  in  other  ways  than  by  direct 
tension.  Copper  wire  is  hardened  by  continual  bending  and  straighten- 
ing; sheet  copper  is  hardened  by  hammering  or  by  cold  rolling;  pipes 
may  be  hardened  by  planishing  or  by  being  hammered  or  bent  whilst 
they  are  '  loaded/  and  copper  tubes  are  always  hardened  when  they  are 
drawn  on  a  draw-bench  either  to  a  smaller  diameter  or  a  thinner  gauge. 
In  whatever  way  copper  is  hardened,  its  ductility  is  correspondingly 
lessened,  and  in  all  cases  the  hardening  may  be  removed  by  '  annealing/ 
that  is,  by  raising  it  to  a  bright-red  heat,  and  either  quenching  it  in 
water  or  allowing  it  to  cool  gradually. 

"  Commercial  copper,  as  used  for  other  than  electrical  purposes,  is 
rarely  pure,  or  even  nearly  pure.  The  effects  of  some  of  the  common 
impurities,  such  as  arsenic,  nickel,  and  silver,  are  supposed  not  to  be 
detrimental;  while,  on  the  other  hand,  antimony  is  objectionable,  and 
bismuth,  even  in  small  traces,  is  exceedingly  prejudicial.  The  usual 
workshop  test  for  the  quality  of  copper  is  to  cut  off  a  portion  of  the  pipe 
or  sheet  and  anneal  it,  when  it  should  stand  bending  quite  close  without 
a  sign  of  cracking.  The  edges  also  should  stand  thinning  to  a  knife- 
edge  without  cracking-  when  hammered  to  a  scarf-joint  form  with  a  lap 
of  about  three  or  four  times  the  thickness  of  the  copper. 


152  STEAM-BOILERS 

"  Brazing.  Brazing-solder  is  composed  of  copper  and  zinc  in 
about  equal  proportions;  occasionally,  however,  one-half  per  cent  of 
tin  is  added  to  the  mixture.  The  mixed  metal  is  first  cast  in  iron  ingot- 
moulds,  then  it  is  reheated  to  a  certain  temperature,  considerably  below 
red  heat,  at  which  it  becomes  brittle  and  is  pounded  up  with  an  iron 
pestle  and  mortar.  The  addition  of  the  small  quantity  of  tin  is  said  to 
facilitate  the  pounding.  It  thus  appears  that  at  a  temperature  inter- 
mediate between  that  of  the  steam  and  a  red  heat  the  solder  becomes 
brittle  and  unfit  to  sustain  any  stress. 

"  It  usually  is  considered  that  the  brazing-solder,  like  copper,  is  not 
liable  to  corrosion,  and  in  the  majority  of  cases  in  which  brazed  copper 
steam-pipes  have  been  cut  up  after  many  years  of  service  the  brazing 
is  found  to  be  in  as  good  condition  as  the  copper.  In  a  few  cases,  however, 
the  brazing  of  copper  steam-pipes  has  been  found  to  have  deteriorated 
in  use  to  an  alarming  extent.  Attention  was  first  drawn  to  this  in  the 
case  of  the  fatal  explosion  of  the  steam-pipe  of  the  S.  S.  "  Prodano."  After 
the  official  inquiry  into  the  matter  this  case  was  investigated  by  Pro- 
fessor Arnold  of  Sheffield,  whose  report  was  published  in  Engineering, 
Vol.  LXV,  p.  468,  and  The  Engineer,  Vol.  LXXXV,  p.  363.  Professor 
Arnold  showed  that  the  brazing  in  this  and  in  another  case  submitted 
to  him  at  the  same  time  had  deteriorated  by  the  whole  of  the  zinc  in 
some  parts  of  the  solder  becoming  oxidized,  the  copper  remaining  in 
the  form  of  a  spongy  metallic  mass,  the  pores  of  wrhich  were  filled  with 
oxidized  zinc.  He  attributed  this  result  to  electrolytic  action  set  up 
by  fatty  acids  produced  in  the  boiler  or  in  the  steam-pipe  from  the 
decomposition  of  organic  oils,  as  he  found  and  separated  these  organic 
acids  from  the  deteriorated  solder.  Since  attention  was  drawn  to  these 
cases  a  few  other  steam-pipes  have  been  found  to  have  similarly  depre- 
ciated in  their  brazing. 

"  It  is  worthy  of  note  that  experience  with  Muntz's  metal  exposed  to 
the  corrosive  action  of  sea-water  shows  that  a  somewhat  similar  de- 
terioration of  the  zinc  takes  place.  It  is  said  that  this  is  prevented  if  a 
small  quantity  of  tin  is  added  to  the  mixture;  but  in  the  cases  of  the 
brazing-solder  investigated  by  Professor  Arnold,  one  specimen,  which 
originally  contained  one-half  per  cent  of  tin,  was  equally  affected  to  that 
composed  of  copper  and  zinc  only." 

Brass.     Brass  is  an  alloy  of  copper  and  zinc. 

Bronze  is  an  alloy  of  copper  and  tin,  or  of  copper  and  tin  with 
zinc  or  some  other  metal.  Many  of  the  bronzes  are  commonly 
called  "brass." 

In  boiler  construction  brass  is  chiefly  limited  to  tubes,  flanges 
for  pipes  and  boiler-mountings. 


MATERIALS  153 

Brass  boiler-tubes  are  used  but  little,  except  in  some  naval 
boilers  and  in  feed-water  heaters.  It  then,  usually,  has  a  com- 
position of  68  per  cent  of  best  selected  copper  and  32  per  cent  of 
zinc.  Its  tensile  strength  exceeds  66,000  pounds  per  square  inch. 

Ordinary  brass  or  yellow  brass,  composed  of  two  parts  of  copper 
and  one  part  of  zinc,  has  a  tensile  strength  of  from  21,000  pounds 
to  27,000  pounds,  and  is  consequently  too  soft  for  anything  but 
ornamental  purposes. 

Boiler-mountings  may  be  made  of  Muntz's  metal,  composed 
of  three  parts  of  copper  and  two  of  zinc,  which  is  very  ductile  and 
has  a  strength  of  about  45,000  pounds;  or  of  naval  brass,  which 
is  made  by  adding  about  one  per  cent  of  tin  to  Muntz's  metal. 
This  naval  brass  is  quite  as  strong  as'Muntz's  metal  and  superior 
to  it  in  ductility,  and  will  resist  the  action  of  salt  water. 

The  strengths  of  both  are  increased  when  rolled  or  forged  and 
annealed,  but  are  less  than  the  above  figure  when  cast. 


CHAPTER  VIII 
BOILER  DETAILS 

The  Shell.  Strength  of  Shell,  Longitudinally  and  Transversely.  Fac- 
tor of  Safety.  Rules  for  Thickness  of  Shell.  Limits  of  Thickness.  Arrange- 
ments of  Plates.  The  Ends.  Rules  for  Thickness  of  Heads.  Flat  Surfaces. 
Rules  for  Flat  Surfaces.  Flues.  Strengthening  Rings.  Corrugated  and 
Ribbed  Flues.  Rules  for  Flues  and  Liners.  Tubes.  Rules  for  Thickness. 
Stays.  Rules  for  Stays.  Girders.  Combustion-chamber.  Riveting. 
Welding.  Setting.  Bridge  Wall.  Split  Bridge. 

The  Shell.  The  pressure  of  steam,  or  of  any  gas,  enclosed  in  a 
cylindrical  shell  is  exerted  equally  in  all  directions,  and  is  at  right 
angles  to  the  surface  and  therefore  along  radial  lines.  The  pressure 
tends  to  enlarge  the  vessel  and  to  keep  it  in  the  true  cylindrical 
form.  It  is  resisted  by  the  strength  of  the  metal,  the  tendency 
being  to  create  rupture  longitudinally. 

As  the  metal  is  never  absolutely  homogeneous,  the  rupture 
commences  at  some  weak  point,  but  does  not  always  follow  the 
line  of  least  resistance,  because  the  final  failure  takes  place  so 
suddenly  that  not  only  does  time  become  an  element,  but  also 
new  and  undeterminable  stresses  are  introduced. 

Let  A B  in  Fig.  37  be  any  diameter  of  the  circle  whose  centre  is  at 
0,  and  which  may  represent  the  section  of  a  cylindrical  boiler-shell. 
Let  xy  represent  a  very  small  length  of  the  section,  which  may  be 
considered  as  straight  without  any  appreciable  error.  The  pressure 
exerted  on  this  area  xy  can  be  represented  in  direction  and  magni- 
tude by  pxy,  p  being,  the  pressure  per  unit  of  area.  Resolve  this 
force  into  its  two  components,  one  perpendicular  and  one  parallel 
to  the  diameter  AB,  and  denote  the  angle  between  the  direction  of 
xy  and  AB  by  a-.  The  vertical  component  is  then  p.xy  cos  a. 
But  xy  cos  a  is  equal  to  the  projection  of  xy  on  the  diameter  AB. 
If  the  same  analysis  were  made  for  every  point  of  the  semi-circum- 
ference; then  the  algebraic  sum  would  be  ly  xy  cos  a  equal  to 

154 


BOILER  DETAILS 


155 


p  .  AB.     In  other  words,  the  sum  of  all  the  perpendicular  com- 
ponents is  equal  to  the  unit  of  pressure  times  the  diameter,  and 
this  is  the  force  tending 
to  produce  rupture  along 
the  longitudinal  lines  at  A 
and  B. 

The  parallel  compo- 
nents, being  equally  dis- 
tributed on  each  side, 
neutralize  one  another,  are 
therefore  inert  and  have 
no  effect  on  the  stresses 
at  A  and  B. 

The  cylinder  resists 
rupture  by  an  amount 
equal  to  the  area  of  the 
metal  at  A  and  B  times 
the  tensile  strength  of  the 
material.  (This  statement  is  only  true  for  cylinders  whose  thick- 
ness is  very  small  in  comparison  with  the  diameter,  and  the 
following  analysis  fails  for  all  cases  where  the  diameter  is  small  and 
the  thickness  large,  as  in  cannon  or  hydraulic  cylinders.  This  is 
due  to  the  elasticity  of  the  material,  which  in  thick  shells  would 
allow  the  inner  layers  to  be  stretched  to  an  injurious  amount 
before  the  outer  ones  had  reached  their  elastic  limit.) 

At  the  moment  of  rupture,  denoting  the  bursting  pressure  by 
P  pounds  per  unit  of  force,  the  force  of  the  gas  and  the  resisting 
strength  of  the  shell  are  equal,  and  consequently 

PXDX  Length  =  2X*XcX  Length. 

2tc 
~  D' 


FIG.  37. — Strength  of  shell  to  resist 
bursting  pressure. 


2c' 


in  which  c  denotes  the  tensile  strength. 

It  is  to  be  noted  that  the  strength  of  a  shell  to  resist  bursting  is 
independent  of  the  length;  but,  as  will  be  seen  later,  the  length 
plays  a  very  important  part  in  the  strength  when  contraction  and 


156  STEAM-BOILERS 

expansion  are  considered,  as  also  when  the  pressure  is  external  to 
the  shell  tending  to  produce  failure  by  collapsing. 

In  a  boiler-shell  with  lap-jointed  plates  the  perfect  cylindrical 
form  cannot  be  obtained,  but  since  the  distortion  is  very  small,  the 
weakness  is  more  due  to  the  uneven  distribution  of  the  stress  on  the 
rivets  of  the  joint  than  to  the  lack  of  a  perfect  cylindrical  section. 

The  ends  of  the  cylinder,  especially  when  flat,  act  like  stays,  and 
must  give  it  increased  strength.  How  much  increase  in  strength 
or  how  far  from  the  ends  does  this  end  influence  extend  is  unknown, 
but  in  boilers  having  a  short  longitudinal  dimension  compared  to 
diameter  the  influence  may  be  considerable.  (Reference  is  made 
to  a  paper  by  J.  G.  Spence,  Trans.  North-east  Coast  Institution  of 
Engineers  and  Shipbuilders,  and  discussion  in  Engineering,  1891 
et  seq.). 

In  oval  boilers  this  additional  strength  due  to  the  ends  is  im- 
portant, but  on  account  of  the  high  modern  pressures  oval  boilers 
are  seldom  used. 

In  practice  no  allowance  is  made  for  the  strength  imparted  by 
the  ends,  due  to  its  uncertain  character.  Since  undeterminable 
conditions  often  exist,  due  to  faults  in  staying,  poor  joints,  flaws 
and  corrosion,  all  of  which  cannot  be  allowed  for  with  accuracy,  this 
increase  in  strength  is  permitted  to  offset,  in  whole  or  in  part,  these 
sources  of  weakness. 

The  stress  tending  to  cause  rupture  transversely  or  in  a  ring 
direction  around  the  boiler  is  the  pressure  on  the  boiler-head.  The 
resisting  strength  is  evidently  that  of  the  circular  section  of  the 
metal. 

At  the  moment  of  rupture  these  forces  are  equal,  and,  using  the 
same  letters  as  before,  can  be  expressed  thus  : 


Neglecting  yr,  since  it  is  always  a  very  small  fraction, 

PD 


BOILER  DETAILS  157 

On  comparing  this  result  with  that  obtained  for  longitudinal  rup- 
ture, it  will  be  noted  that  any  shell  of  uniform  thickness  is  twice  as 
strong  transversely  as  longitudinally,  and  that  if  the  metal  be  cal- 
culated for  thickness  in  the  latter  direction  it  will  be  amply  heavy 
to  resist  in  the  former  direction.  On  account  of  wear  due  to  buck- 
ling from  expansion  and  the  consequent  tendency  to  groove  and 
corrode,  boilers  often  fail  on  the  ring  seams,  so  that  these  seams 
demand  as  much  care  in  proportioning  as  the  longitudinal  ones, 
although  not  subjected  to  so  heavy  a  stress. 

Due  to  the  difference  in  stress,  it  is  quite  common  to  rivet  the 
longitudinal  seams  more  strongly  than  the  ring  seams. 

External  Pressure  on  a  Stayed  Shell.  In  cases  where  the 
pressure  is  external  to  a  cylinder  which  is  supported  by  stay-bolts, 
as  for  example  the  inner  shell  or  furnace  of  a  vertical  boiler,  it 
would  be  well  to  call  attention  to  the  conclusions  stated  in  Locomo- 
tive, March,  1892: 

(1)  The  stresses  in  the  plates  of  a  curved  water-leg  are  never  greatly 
different  (at  the  usual  working  pressures)  from  those  that  prevail  in  a 
similarly  designed  flat-stayed  surface ;  (2)  The  curved  form  of  the  leg  does, 
however,  cause  the  tension  on  the  outer  sheet  to  be  somewhat  greater 
than  it  would  be  in  a  flat  leg;  (3)  The  stress  on  the  inner  sheet  is  never 
a  compression,  but  always  a  tension;  (4)  This  tension  on  the  inner  sheet 
will  differ  (usually  by  a  small  amount)  from  the  tension  on  a  similar  flat 
stay-bolted  sheet,  being  sometimes  greater  and  sometimes  less,  according 
to  the  designs  and  proportions  of  the  water-leg;  and  (5)  The  curvature 
of  the  leg  causes  the  stress  on  the  stay-bolts  to  be  somewhat  less  than  it 
would  be  on  a  similar  flat  leg. 

Factor  of  Safety.  The  proper  factor  to  use  in  determining  the 
thickness  of  a  boiler-shell  is  open  to  dispute.  It  is  evident  that  it 
should  be  as  small  as  safety  will  permit,  and  its  selection  should 
depend  on  the  quality  of  metal  used,  on  the  methods  adopted  in 
construction  and  on  the  efficiency  of  the  workmanship  employed. 
Probably  under  good  inspection  and  with  careful  builders  a  factor 
of  safety  of  three  is  sufficient,  but  this  factor  should  be  taken  on  the 
weakest  part,  which  is  usually  the  joint,  and  not  on  the  strength  of 
the  shell  plating. 

Rules  for  Thickness  of  Shell.  There  can  be  little  question  as 
to  the  advisability  of  proportioning  the  thickness  on  the  elastic 
limit  of  the  metal  rather  than  on  the  ultimate  strength. 


158  STEAM-BOILERS 

While  a  boiler  may  not  burst  when  the  elastic  limit  has  been 
exceeded,  still  the  shell  has  practically  failed,  due  to  the  permanent 
distortion  which  has  taken  place  and  which  will  reduce  the  actual 
strength.  There  is,  however,  a  commercial  disadvantage  in  the 
use  of  elastic  limit,  since  so  many  boilers  are  made  of  sheets  of  which 
this  property  is  not  known,  although  the  plates  could  be  as  easily 
tested  for  the  elastic  limit  as  for  ultimate  tensile  strength. 

1.  Rule   of   U.  S.  Board  of   Supervising   Inspectors  of  Steam- 
vessels. — Multiply   one-sixth   Q)  of  the   lowest    tensile    strength 
found  stamped  on  any  plate  in  the  cylindrical  shell  by  the  thick- 
ness— expressed  in  inches  or  parts  of  an  inch — of  the  thinnest 
plate  in  the  same  cylindrical  shell,  and  divide  by  the  radius  or  half 
diameter — also  expressed  in  inches — and  the  result  will  be  the  pres- 
sure   allowable  per  square  inch  of  surface  for  single-riveting,  to 
which  add  20  per  cent  for  double-riveting,  when  all  the  rivet  holes 
in  the  shell  of  such  boiler  have  been  " fairly  drilled"  and  no  part 
of  such  hole  has  been  punched. 

This  rule  is  the  one  most  commonly  employed  in  this  country, 
but  is  very  defective.  It  does  not  consider  workmanship  or  the 
strength  of  joint,  which  is  the  real  strength  of  the  shell.  The  same 
thickness  would  be  used  for  a  well-proportioned  joint  as  for  a  poor 
one. 

2.  Rule   of   Lloyd's  Registry   (British). — For    steel    cylindrical 
boiler-shells, 

Working  pressure  in  pounds  |         __  constant X  (t  —  2)XB 


per  square  inch  • ) 

in  which  D  denotes  mean  diameter  of  shell  in  inches; 

t         "        thickness  of    plate    in   sixteenths  of   an  inch 

expressed  as  a  whole  number; 

Constant  is  21  when  the  longitudinal  seams  are  fitted 
with  double  butt-straps  of  equal  width; 
Constant  is  20.25  when  they  are  fitted  with  double  butt- 
straps  of  unequal  width,  only  covering, 
on  one  side  the  reduced  section  of 
plate  at  the  outer  lines  of  rivets; 

Constant  is  19.5  when  the  longitudinal  seams  are  lap-joints; 
B  denotes  the  least  percentage  of  strength  of  longitudinal 
joint. 


BOILER  DETAILS  159 

Note.  —  For  shell  plates  of  super-heaters  or  steam-chests  en- 
closed in  the  uptake  or  exposed  to  the  direction  of  the  flame  the 
constants  should  be  two-thirds  of  those  given  above.  The 
material  to  have  an  ultimate  tensile  strength  of  not  less  than 
58,240  pounds  and  not  more  than  67,200  pounds  per  square  inch 
of  section. 

The  value  cf  B  can  be  found  as  follows,  the  least  value  being 
taken: 

7)  —  d 
For  percentage  of  plate  at  joint,  B  =  —   —  X103, 


rivets 


in  which  t  denotes  thickness  of  plate  in  inches  ; 
p        "       pitch  of  rivets  in  inches; 
d        "       diameter  of  rivet  holes  in  inches; 
a        "       sectional  area  of  rivets  in  inches; 
n        "       number  of  rows  of  rivets; 
F       "        100  when  rivets  are  iron  and  plates  are  iron, 

holes  punched; 
F       "       90  when  rivets  are  iron  and  plates  are  iron,  holes 

drilled; 
F       "       85  when  rivets  are  steel  and  plates  are  steel, 

holes  drilled; 
F       "       70  when   rivets  are  iron   and  plates  are  steel, 

holes  drilled. 

Note.  —  If  rivets  are  in  double  shear,  use  1.75a  instead  of  a. 
There  are  other  rules,  such  as  Board  of  Trade  (British),  Bureau 
Veritas,  German  Lloyds,  etc.  Certain  cities  have  rules  for  local 
inspection,  as  have  the  various  boiler-insurance  companies.  Many 
authors  have  advanced  rules  of  their  own,  but  they  are  chiefly 
modifications  of  the  principal  ones  above  mentioned. 

Reference  is  made  to  a  criticism  of  the  rules  used  for  marine 
boilers  (which  applies  equally  to  land  boilers)  in  a  paper  by  Nelson 
Foley,  published  in  Transactions  of  Division  of  Marine  and  Naval 
Engineering,  Chicago  Engineering  Congress,  1893,  and  to  a  paper 
by  the  author,  Trans.  Am.  Soc.  Mechanical  Engineers,  Vol.  XXII, 
p.  127,  1901. 


160  STEAM-BOILERS 

Many  engineers  place  the  minimum  thickness  of  shell  for  exter- 
nally fired  boilers  at  f  of  an  inch,  because  thin  sheets  exposed  to 
sudden  extreme  variations  of  temperature  lose  in  elasticity,  and  will 
corrode  as  much  as  thick  ones,  so  that  the  percentage  of  loss  of 
strength  will  be  much  greater. 

The  maximum  thickness  is  usually  limited  to  f  or  f  inch.  The 
thickness  is  controlled  by  the  liability  to  burn  in  externally  fired 
boilers.  In  shells  not  exposed  to  the  fire  the  thickness  is  only 
limited  by  the  appliances  of  the  boiler-shop.  There  are  few  boiler- 
shops  equipped  to  properly  handle  sheets  exceeding  1J  inches  in 
thickness.  Also,  thick  sheets  are  difficult  to  rivet,  as  the  size  of 
rivet  is  limited,  and  small  rivets  in  thick  sheets  necessitate  too  much 
cutting  of  the  plates  in  order  to  procure  a  high  efficiency  of  joint. 
When  the  shell  of  externally  fired  boilers  is  very  thick,  the  life 
of  the  boiler  may  be  prolonged  by  constructing  a  fire-brick  arch 
over  the  furnace.  Such  an  arch  assists  the  combustion  by  prevent- 
ing the  products  from  becoming  chilled,  and  also  shields  the  crown- 
sheet  from  impingement  of  cold  air  through  the  fire-doors.  When 
used,  however,  care  must  be  taken  not  to  bury  the  boiler  in  masonry, 
but  arrange  for  inspection  of  the  covered  portion  of  the  boiler. 
Oftentimes  this  only  can  be  done  by  so  constructing  the  arch  that 
it  will  not  come  into  actual  contact  with  the  shell,  and  that  it  may 
be  removed  for  inspection  and  repair  without  disarranging  the  rest 
of  the  setting. 

Arrange  the  sheets  so  as  to  keep  the  seams  as  far  as  possible  from 
the  direct  action  of  the  fire.  This  cannot  always  be  accomplished 
with  ring-seams  of  externally  fired  boilers,  except  by  the  use  of  very 
large  sheets,  the  cost  of  which  may  be  prohibitive.  In  such  boilers 
the  longitudinal  seams  can  usually  be  placed  out  of  reach  of  the  fire 
without  complication.  When  lap-seams  must  be  exposed  to  the 
passage  of  the  hot  gases,  arrange  so  that  the  gases  do  not  strike 
against  the  edge  of  the  lapping  plate.  In  like  manner  arrange  the 
lap-seams  so  that,  the  circulation  or  convection  currents  will  not 
strike  against  a  lapping  edge,  upon  which  the  sediment  may  lodge. 
The  lack  of  this  precaution  has  often  caused  a  crown-plate  to  bulge 
downward. 

Place  the  plates  so  that  the  direction  in  which  they  were  rolled 
shall  be  circumferential,  that  the  direction  of  greatest  strength  shall 
be  in  line  with  the  greatest  stress. 


BOILER   DETAILS  161 

Make  use  of  as  large  sheets  as  possible,  so  as  to  reduce  the  number 
of  seams.  Boiler-plates  seldom  are  made  larger  than  121  inches  in 
width,  but  can  be  procured  of  any  reasonable  length.  The  length 
usually  is  limited  to  about  33  feet,  which  is  the  length  of  the  plat- 
form of  a  freight-car.  Plates  are  not  available  for  their  full  length 
or  width,  as  the  edges  of  the  sheets  are  usually  the  weakest  parts 
and  are  most  liable  to  carry  defects,  and  it  is  near  the  edges  that 
the  line  of  rivets  must  come.  Plates  should  be  trimmed  off  on  each 
side  by  at  least  3^  to  4  inches  for  careful  work. 

Arrange  the  longitudinal  seams  so  as  to  break  continuity  at  the 
circumferential  seams,  as  thereby  increased  shell  strength  is 
obtained.  These  longitudinal  seams  in  adjacent  courses  of  plates 
should  be  separated  as  far  apart  as  can  be  arranged  conveniently, 
but  when  prevented  by  other  reasons  the  centre  lines  of  the  seams 
may  be  as  near  as  the  pitch  of  three  rivets.  At  such  places  three 
plates  must  overlap,  and  the  corner  of  the  middle  plate  is  forged 
thin,  tapering  like  a  wedge,  so  that  the  other  plates  may  come 
gradually  into  contact  and  be  calked. 

The  successive  courses  in  long  boilers  are  best  made  parallel; 
that  is,  one  course  is  an  outer  course,  the  second  laps  under  the  first 
and  third,  forming  an  inner  course,  and  so  on  alternately  inside  and 
outside.  By  this  arrangement  the  brick  setting  is  also  least  apt 
to  be  disturbed  by  the  expansion  of  the  boiler.  Sometimes  the 
courses  are  parallel,  but  each  successive  course  is  arranged  as  an 
inner  course  to  the  one  preceding  and  as  an  outer  course  to  the  one 
following.  This  method  is  adopted  in  some  locomotive  boilers,  the 
largest  course  being  at  the  fire-box  end.  Occasionally  the  courses 
are  arranged  conically;  that  is,  as  an  outside  course  to  the  one  pre- 
ceding and  as  an  inner  course  to  the  one  following.  The  objection 
to  this  latter  method  is  the  difficulty  of  cutting  the  sheets,  as  they 
will  not  be  rectangular,  and  the  danger  of  the  rivet-holes  not  match- 
ing fair.  They  are  also  more  liable  to  disarrangement  from  expan- 
sion and  contraction  than  when  the  sheets  are  parallel. 

In  vertical  boilers  it  is  best  to  arrange  the  lap  of  horizontal  ring- 
seams  to  face  downward  on  the  inside,  so  as  to  prevent  sediment 
from  catching. 

Whatever  arrangement  is  adopted,  the  shell  should  be  so  placed 
as  to  drain  itself  when  required.  This  is  accomplished  by  setting 
the  shell  lower  at  the  end  where  the  bottom  blow-off  is  located.  In 


162  STEAM-BOILERS 

general  a  difference  of  from  1  inch  to  2  inches  in  25  feet  of  length  is 
sufficient. 

The  Heads.  It  is  obvious  that  the  best  form  for  resisting  in- 
ternal pressure  is  the  sphere;  and,  further,  the  pressure  will  always 
tend  to  preserve  the  true  spherical  form,  which  will  therefore  be 
self-supporting. 

The  pressure  tending  to  burst  a  sphere  along  the  intersection  of 
any  plane  passing  through  its  centre  is  measured  by  the  pressure  per 
unit  of  surface  times  the  area  of  such  a  plane,  which  force  may  be 
expressed  thus : 

p«£ 

N  4 

The  resistance  to  rupture  is  the  strength  of  the  metal  at  the  place 
of  intersection  of  the  plane,  which  may  be  expressed  thus: 

n(D+t)tc. 
At  the  instant  of  rupture  these  quantities  are  equal. 

xD2 
P~-=n(D+t)tc. 

Dividing  by  xD,  and  neglecting  ^,  which  is  always  a  small  fraction 

in  boiler  construction,  the  expressions  for  bursting  pressure  and 
thickness  become 

p     4tc  PD 

P=-j^     and      t  =  ——. 
D  4c 

These  are  the  same  results  as  were  obtained  for  the  transverse 
strength  of  the  cylinder;  so  that  the  sphere  is  twice  as  strong  as  is 
the  cylinder  longitudinally,  when  the  diameters  are  equal. 

Advantage  of  this  fact,  as  well  as  of  the  self-sustaining  property, 
is  taken  in  making  the  heads  of  many  boilers  portions  of  a  sphere. 
When  the  diameter  of  the  sphere  of  which  the  head  is  part  is  twice 
the  diameter  of  the  cylinder,  the  strength  of  shell  and  head  will  be 
equal  to  resist  bursting.  On  the  other  hand,  the  less  the  diameter 
of  the  spherical  heads,  the  less  will  be  their  efficiency  in  strengthening 
the  cylindrical  shell. 

In  all  plain  cylindrical  boilers  the  heads  are  always  thus  made, 


BOILER   DETAILS  163 

and  such  heads  are  said  to  be  "cambered,"  or  "dished,"  or 
"  bumped, "  see  Fig.  9. 

All  boiler-heads  would  be  made  cambered  if  it  were  not  for  the 
difficulty  of  obtaining  tight  joints  with  tubes  and  flues.  In  many 
Scotch  or  drum  boilers  the  heads  are  made  part  cylindrical  above 
the  top  row  of  tubes,  thus  avoiding  heavy  stays  in  the  steam-space, 
see  Fig.  22. 

The  heads,  whether  flat  or  cambered,  are  best  fastened  to  the 
shell  by  flanging  the  end  sheets  so  as  to  pass  on  the  inside  of  the 
shell  plating.  The  flanging  should  be  over  a  radius  about  2J  times 
the  thickness.  The  flange  should  be  single-riveted  to  the  shell 
when  the  circumferential  seams  are  double-riveted,  and  should  be 
double-riveted  when  those  seams  are  treble-riveted  or  quadruple- 
riveted;  although  every  case  should  be  considered  by  itself,  as  much 
depends  on  the  bracing  of  the  head  by  the  stays. 

When  flat  heads  are  used,  one  end  is  best  flanged  in  and  the  other 
out,  so  that  both  may  be  closed  by  the  power-riveter.  When  both 
heads  are  flanged  inward,  the  head  put  on  last  must  be  hand- 
riveted.  With  externally  fired,  return- tubular  or  flue  boilers  the 
rear  heads  should  be  flanged  in,  so  as  not  to  expose  the  unprotected 
thin  edge  of  the  joint  to  the  action  of  the  hot  gases.  With  an 
extended  smoke-box  the  front  head  may  be  flanged  out.  The  head 
may  be  fastened  by  an  angle,  but  flanging  is  much  better,  being  less 
liable  to  suffer  from  corrosion  or  grooving. 

When  an  angle  is  used,  it  should  be  put  on  the  outside  of  the  shell, 
at  least  at  one  end.  and  better  on  both  unless  the  back  head  be 
exposed  to  the  returning  hot  gases,  as  in  Lancashire  and  Cornish 
boilers.  The  internal  angle  forms  too  stiff  an  attachment,  since  the 
distance  from  the  row  of  rivets  to  the  nearest  flue  is  so  short.  The 
external  angle  makes  this  distance  longer,  and  allows  the  head  to 
spring  so  as  to  relieve  the  joint  and  prevent  grooving,  when  the 
pressure  is  brought  upon  the  head  by  expansion  of  the  flue.  It  is 
very  desirable  that  flat  heads  be  not  made  too  stiff,  in  order  that 
they  may  spring  sufficiently  to  relieve  the  local  strains  caused  by 
expansion  and  contraction. 

It  is  best  to  make  the  head  out  of  one  sheet  when  possible. 
In  large  boilers  this  is  offlen  impossible,  and  the  head  must  be 
made  of  two  or  more  pieces  joined  together  by  rivets.  The  seam 
is  usually  made  lapped,  and  its  position  selected  to  suit  the  gen- 


164  STEAM-BOILERS 

eral  design.  No  rule  can  be  stated  for  single-  or  double-riveting 
this  joint,  selection  depending  on  the  judgment  of  the  designer 
and  the  method  of  staying.  Often  this  lap  can  be  so  arranged  as 
to  receive  the  ends  of  some  of  the  stays,  and  thus  dispense  with 
washers  required  by  the  rules  for  flat  surfaces. 

Rules  for  Thickness  of  Heads.  For  "cambered"  or  " dished" 
heads  the  thickness  or  pressure  may  be  calculated  by  the  rules  given 
for  cylinders,  but  using  the  diameter  of  the  sphere,  of  which  the  head 
forms  a  part,  as  the  value  of  D. 

The  U.  S.  Board  of  Supervising  Inspectors  of  Steam-vessels 
states  that  the  pressure  of  steam  per  square  inch  allowed  shall  be 
found  by  multiplying  the  thickness  of  plate  by  one-sixth  of  the 
tensile  strength,  and  dividing  by  one-half  of  the  radius  to  which  the 
head  is  bumped.  Where  the  heads  are  concaved,  multiply  the  pres- 
sure per  square  inch  found  for  similar  bumped  heads  by  six-tenths, 
and  the  result  will  be  the  steam-pressure  allowable. 

On  unstayed  flat  heads,  when  flanged  and  made  of  steel,  of 
wrought-iron,  or  of  cast-steel,  the  pressure  per  square  inch  allow- 
able is  determined  by  multiplying  the  thickness  of  plate  in  inches  by 
one-sixth  the  tensile  strength  in  pounds,  and  dividing  by  the  area 
of  the  head  in  square  inches  multiplied  by  nine  one-hundredths. 

Flat  heads  supported  by  stays  are  proportioned  by  the  rules  for 
flat  surfaces. 

Flat  Surfaces.  Many  parts  of  a  boiler  must  necessarily  be 
made  of  flat  plates.  In  order  to  make  them  self-supporting,  they 
need  be  so  thick  as  to  be  impracticable.  In  consequence  they  are 
strengthened  or  supported  in  various  ways,  but  most  commonly  by 
stays. 

The  formula  adopted  is  based  upon  that  for  beams;  the  portion 
of  the  plate  lying  between  the  rows  of  stays  being  taken  as  equiva- 
lent to  a  beam,  rectangular  in  section,  fixed  at  the  ends  and  uni- 
formly loaded,  any  extra  strength  due  to  end  connections  being 
neglected. 

Flat  surfaces  should  be  avoided  as  much  as  possible,  as  not 
only  being  an  element  weak  per  se,  but  also  rendering  difficult  the 
cleaning  and  inspection  from  the  numerous  stays  that  are  required. 

The  end  plates  of  boilers,  in  the  steam-space,  where  not  subjected 
to  contact  with  hot  gases,  are  frequently  strengthened  by  riveting 
to  them  a  "  doubling-plate."  Where  the  rivets  are  not  spaced 


BOILER  DETAILS  165 

farther  apart  than  the  distance  allowed  for  bolts  on  a  flat  surface, 
the  plate  is  considered  of  extra  thickness,  so  that  the  stays  may  be 
spaced  far  enough  apart  to  permit  a  man  to  pass  between  them. 
(See  rules  given  below.)  Such  doubling-plates  are  used  chiefly  on 
Scotch  boilers  designed  for  high  pressures.  In  ordinary  land  or 
stationary  boilers  the  heads  are  stayed  to  the  shell  by  gusset-plates 
and  diagonal  stays,  which  do  not  interfere  with  entrance  through 
the  manhole  above  the  tubes,  as  would  the  " through  and  through" 
stays  from  head  to  head. 

The  flat  tube-sheets  are  sufficiently  supported  by  the  tubes 
when  they  are  expanded  and  have  ends  " beaded  over"  or  " flared." 
When  very  high  pressures  are  used  it  is  well  to  make  some  of  the 
tubes  as  stay-tubes  and  thus  provide  additional  support.  This  is 
the  practice  in  many  marine  boilers.  The  space  between  the  nests 
of  tubes,  and  between  outer  tubes  and  side  of  shell,  as  also  between 
furnace-flues,  must  be  stayed,  or  thickness  made  sufficient  for  the 
pressure  required.  These  latter  spaces  often  are  strengthened  by 
angles  or  tees  riveted  to  the  flat  surfaces.  (See  rules  below  and  also 
"Stays.")  Tube-sheets  should  never  be  less  than  f-inch  thick, 
so  that  the  tubes  may  be  cut  out  and  new  ones  put  in  without 
injury  to  the  plate. 

Rules  for  Flat  Surfaces. 
1.   U.  S.  Board  of  Supervising  Inspectors  of  Steam-vessels. 

The  flat  surface  at  back  connection  or  back  end  of  boilers  may  be 
stayed  by  the  use  of  a  tube,  the  ends  of  which  being  expanded  in  holes 
in  each  sheet  beaded  and  further  secured  by  a  bolt  passing  through  the 
tube  and  secured  by  a  nut.  An  allowance  of  steam  shall  be  given  from 
the  outside  diameter  of  pipe.  For  instance,  if  the  pipe  used  be  1|  inches 
diameter  outside,  with  a  l^-inch  bolt  through  it,  the  allowance  will  be 
the  same  as  if  a  l^-inch  bolt  were  used  in  lieu  of  the  pipe  and  bolt.  And 
no  brace  or  stay-bolt  used  in  a  marine  boiler  will  be  allowed  to  be  placed 
more  than  10£  inches  from  centre  to  centre  to  brace  flat  surfaces  on  fire- 
boxes, furnaces,  and  back  connections;  nor  on  these  at  a  greater  dis- 
tance than  will  be  determined  by  the  following  formulas. 

Flat  surfaces  on  heads  of  boilers  may  be  stiffened  with  doubling- 
plate,  tees,  or  angles. 

The  working  pressure  allowed  on  flat  surfaces  fitted  with  screw 
stay-bolts  riveted  over,  screw  stay-bolts  and  nuts,  or  plain  bolt  with 


166  STEAM-BOILERS 

single  nut  and  socket,  or  riveted  head  and  socket,  will  be  determined 
by  the  following  rule: 

When  plates  yV  inch  thick  and  under  are  used  in  the  construction 
of  marine  boilers,  using  112  as  a  constant,  multiply  this  by  the  square 
of  the  thickness  of  plate  in  sixteenths  of  an  inch.  Divide  this  product 
by  the  square  of  the  pitch  or  distance  from  centre  to  centre  of  stay-bolt. 

EXAMPLE.  Plate  rg  inch  thick  with  socket  bolts  or  stay,  6-inch  cen- 
tre, would  be  112,  the  constant,  multiplied  by  the  square  of  7,  the  thick- 
ness of  the  plates  in  sixteenths,  which  is  49,  would  give  5488,  which, 
divided  by  the  square  of  6,  which  is  36,  being  the  distance  from  centre 
to  centre  of  stays  or  the  pitch,  would  be  152,  the  working  pressure  al- 
lowed, provided  the  strain  on  stay  or  bolt  does  not  exceed  6000  pounds 
per  square  inch  of  section. 

Plates  I-  inch  thick,  stay-bolts  spaced  4-inch  centre  =  —     —  =112 


112  X25 
Plates  IB£  inch  thick,  stay-bolts  spaced  5-inch  centre  =  —    —  :  =112 


112X25 

Plates  j5ff  inch  thick,  stay-bolts  spaced  6-inch  centre  =  —  ^  —  :  =   77 


pounds  W.  P. 

Plates  i5ff  : 
pounds  W.  P. 
Plates  T\ 

pounds  W.  P. 

112  X36 
Plates  |  inch  thick,  stay-bolts  spaced  6-inch  centre  =  —  ^  —  =112 

oO 

pounds  W.  P. 

Plates  above  iV  inch  thick  the  pressure  will  be  determined  by  the 
same  rule,  excepting  the  constant  will  be  120;  then  a  plate  £  inch  thick, 
stays  spaced  7  inches  from  centre,  would  be  as  follows:  120,  the  constant, 
multiplied  by  64,  the  square  of  thickness  in  sixteenths  of  an  inch,  equals 
7680,  which,  divided  by  the  square  of  7  inches  (distance  from  centre  to 
centre  of  stays),  which  is  49,  would  give  156  pounds  W.  P. 

Plates  f  or  it  of  an  inch  thick,  spaced  10£  inches,  would  be 

1°0  X  144 
"  =156  pounds  W.  P. 


On  other  flat  surfaces  there  may  be  used  stay-bolts  with  ends  threaded, 
having  nuts  on  same,  both  on  the  outside  and  inside  of  plates.  The 
working  pressure  allowed  would  be  as  follows: 

A  constant  140,  multiplied  by  the  square  of  the  thickness  of  plate 
in  sixteenths  of  an  inch,  this  product  divided  by  the  pitch  or  distance  of 
bolts  from  centre  to  centre,  squared,  gives  working  pressure. 


BOILER  DETAILS  167 

EXAMPLE.    A  plate  f  inch  thick,  supported  by  bolts  14  inches,  would 


be 

140X144 


=  102  pounds  W.  P. 


Same  thickness  of  plate,  with  bolts  12-inch  centres,  would  be 
140X144 


144 


=  140  pounds  W.  P. 


Flat  part  of  boiler-head  plates  when  braced  with  bolts  having  double 
nuts  and  a  washer  at  least  one-half  the  thickness  of  head,  where  wash- 
ers are  riveted  to  the  outside  of  the  head,  and  of  a  size  equal  to  {  of 
the  pitch  of  stay-bolts,  or  where  heads  have  a  stiffening-plate,  either 
on  inside  or  outside,  covering  the  area  braced,  will  equal  the  thick- 
ness of  head  and  washers;  the  head  and  stiffening-plate  being  riveted 
together  with  rivets  spaced  and  of  sufficient  sectional  area  of  rivets  as 
determined  by  this  section  for  socket-bolts,  shall  be  allowed  a  constant 
of  200,  rivets  to  be  spaced  by  thickness  of  washer  on  the  stiffening- 
plate.  Boiler-heads  so  reinforced  will  be  allowed  a  thickness  to  com- 
pute pressure  allowed  of  80  per  cent  of  the  combined  thickness  of  head 
and  washer  or  head  and  stiffening-plate. 

EXAMPLE.  A  boiler-head  plate  £  inch  thick,  with  washers  f  inch 
thick,  and  12£  inches  square,  supported  by  bolts  14-inch  centres,  would 
be  allowed  a  wrorking  steam-pressure  as  follows: 

Thickness  of  plate  and  washer  equals  f  +f  =f  inches;  80  per  cent  of 
which  combined  thickness  equals  ^Xf  inch  =  .9  inch  =  14.4  sixteenths 
of  an  inch. 

Then,  by  rule, 

200X14.42     200X207.36 

142  196         =^11   pounds  W.  P. 

Plates  fitted  with  double  angle-iron  and  riveted  to  plate  with  leaf 
at  least  two-thirds  thickness  of  plate  and  depth  at  least  one-fourth  of 
the  pitch  would  be  allowed  the  same  pressure  as  determined  by  formula 
for  plate  with  washer  riveted  on. 

EXAMPLE.  A  boiler-head  plate  £  inch  thick,  supported  by  angle- 
iron  }  inch  thick  and  3.5  inches  depth  of  leaf,  and  with  bolts  14-inch 
centres,  would  be  allowed  a  working  steam  pressure  as  follows: 

Thickness  of  head  and  leaf  of  angle-iron  equals  £  -}-i=»|-  inches;  80 
per  cent  of  which  combined  thickness  equals  T8j&Xf  inches  =  1  inch  =  16 
sixteenths  inch. 


168  STEAM-BOILERS 

Then,  by  rule, 

200  X162     200X256 
-fiT-       -y^-  =261  pounds  W.  P. 

But  no  flat  surface  shall  be  unsupported  at  a  greater  distance  in 
any  case  than  18  inches,  and  such  flat  surfaces  shall  not  be  of  less  strength 
than  the  shell  of  the  boiler,  and  able  to  resist  the  same  strain  and  pressure 
to  the  square  inch.  In  allowing  the  strain  on  a  screw  stay-bolt,  the 
diameter  of  the  same  shall  be  determined  by  the  diameter  at  the  bottom 
of  the  thread. 

2.  Lloyd's  Registry  (British}. 

C  Xt2 


Working  pressure,  pounds  per  square  inch  = 

>o 

in  which  t  denotes  thickness  of  plate  in  sixteenths  of  an  inch; 

S       "      greatest  pitch  in  inches,  between  centre  of  stays; 

C       "       90  for  plates  fa  thick  and  less,   fitted  with  screw- 

stays  with  riveted  heads; 
C       "       100  for  plates  over   fa,  fitted  with  screw-stays  with 

riveted   heads  ; 
C       "       110   for   plates  fa   and  less,   fitted   with   screw-stays 

and  nuts; 
C       "       120  for  iron  plates  over  fa,  and  for  steel  plates  over 

fa  and  under  fa,  fitted  with  screw-stays  and  nuts; 
C       "       135  for  steel  plates  fa  and  above,   fitted  with  screw- 

stays  and  nuts; 

C       "       140  for  iron  plates  fitted  with  stays  with  double  nuts; 
C       "       150  for  iron  plates  fitted  with  stays  with  double  nuts, 

and  washers  outside  the  plates,  of  at  least  ^  of  the 

pitch  in  diameter  and  £  the  thickness  of  the  plates  ; 
C       "       160   for   iron   plates   fitted   with   stays  with   double 

nuts,  and  washers  riveted  to  the  outside    of    the 

plates,  of  at  least  f  of  the  pitch  in  diameter  and 

£  the  thickness  of  the  plates; 
C       "       175  for  iron  plates  fitted  with  stays  with  double  nuts, 

and  washers  riveted  to  the  outside  of  the  plates, 

when  the  washers  are  at  least  f  of   the   pitch  in 

diameter  and  of  the  same  thickness  as  the  plates. 
For  iron  plates  fitted  with  stays  with  double  nuts,  and  doubling- 
strips  riveted  to  the  outside  of  the  plates,  of  the  same  thickness  as  the 
plates,  and  of  a  width  equal  to  f  the  distance  between  the  rows  of  stays, 


BOILER   DETAILS  169 

C  may  be  taken  as  175  if  S  is  taken  to  be  the  distance  between  the  rows, 
and  190  when  S  is  taken  to  be  the  pitch  between  the  stays  in  the  rows. 

For  steel  plates  other  than  those  for  combustion  chambers  the  values 
of  C  may  be  increased  as  follows  : 

140  increased  to  175 
150  "  "  185 
160  "  "  200 
175  "  "  220 
^190  "  "  240 

If  flat  plates  are  strengthened  with  doubling  plates  securely  riveted 
to  them,  having  a  thickness  of  not  less  than  f  of  that  of  the  plates, 
the  strength  to  be  taken  from 


Working  pressure  in  pounds  per  square  inch 


in  which  t'  denotes  the  thickness  of  doubling-plates  in  sixteenths  of  an 
inch,  expressed  as  a  whole  number. 

Note.  In  the  case  of  front  plates  of  boilers  in  the  steam  space  the 
values  of  C  should  be  reduced  20  per  cent,  unless  the  plates  are  guarded 
from  the  direct  action  of  the  heat. 

For  steel  tube-plates  in  the  nest  of  tubes  the  strength  to  be  taken 
from 

.  140  X*2 

Working  pressure  in  pounds  per  square  inch  =  -  ^  —  , 

in  which  S  denotes  mean  pitch  of  stay-tubes  from  centre  to  centre. 

For  the  wide  water-spaces  between  nests  of  tubes  the  strength  to 
be  taken  from 


Working  pressure  in  pounds  per  square  inch  =  —  ;=r- 

o 

in  which  S  denotes  the  horizontal  distance  from  centre  to  centre  of  the 

bounding  rows  of  tubes; 
C       "       120  when  the  stay-tubes  are  pitched  with  two  plain 

tubes  between  them,  and  are  not  fitted  with  nuts 

outside  the  plates; 

C       "       130  if  they  are  fitted  with  nuts  outside  the  plates; 
C       "       140  if  each  alternate  tube  is  a  stay-tube  not  fitted 

with  nuts; 
C       "       150  if  they  are  fitted  with  nuts  outside  the  plates; 


70  STEAM-BOILERS 

in  which  C  denotes  160  if  every  tube  in  these  rows  is  a  stay -tube  and 

not  fitted  with  nuts; 

C  170  if  every  tube  in  these  rows  is  a  stay-tube  and 

each  alternate  stay-tube  is  fitted  with  nuts  outside 
the  plates. 

The  thickness  of  tube  plates  of  combustion-chambers  in  cases  \vhere 
the  pressure  on  the  top  of  the  chambers  is  borne  by  these  plates  is  not  to 
be  less  than  that  given  by  the  following  rule: 

pXwXs 

If    ===     "M-I-T'J 


in  which  t  denotes  thickness  of  tube-plate  in  sixteenths  of  an  inch; 
p       "      working  pressure  in  pounds  per  square  inch; 
w  width  of  combustion-chamber  over  plates  in  inches; 

s  horizontal  pitch  of  tubes  in  inches; 

d  inside  diameter  of  plain  tubes  in  inches. 

Flues.  In  internally  fired  boilers  the  grates  are  often  con- 
structed inside  of  large  flues ;  and  in  many  others  flues  are  provided 
to  carry  the  products  of  combustion  and  add  heating  surface. 

On  all  such  flues  the  pressure  is  external,  tending  to  cause  failure 
by  collapsing.  The  flue  may  be  considered  as  an  arch,  and  since 
the  pressure  is  the  same  on  all  points,  the  section  should  be  circular 
in  order  to  present  a  uniform  resistance. 

Should  the  section  not  be  perfectly  cylindrical,  the  external  pres- 
sure will  tend  to  increase  the  flatness  and  finally  cause  collapse. 
Thus  external  pressure  acts  in  an  opposite  way  from  internal  pres- 
sure, since  it  tends  to  aggravate  rather  than  diminish  the  weakness 
due  to  any  departure  from  the  true  cylindrical  form.  Therefore 
with  flues  the  strength  imparted  by  the  end  attachment  becomes 
an  important  element  to  assist  in  keeping  the  form ;  and  the  greater 
the  distance  from  the  end,  the  less  will  this  extra  strength  become. 
From  the  foregoing  remarks  it  is  evident  that  length  must  be  an 
element  in  the  strength  of  any  flue  subjected  to  external  pressure. 

Owing  to  the  complexity  of  the  problem,  it  is  practically  impos- 
sible to  calculate  the  stresses  existing  in  any  flue,  and  the  formulae 
accepted  by  engineers  are  based  on  actual  experiment. 

The  formula  of  Sir  William  Fairbairn  is : 

806,300X*2'19 


BOILER  DETAILS  171 

in  which  P  denotes  the  collapsing  pressure  per  square  inch; 

t  li    thickness  in  inches ; 

d       "          "    diameter    "       "     ; 

L       "          "    length  in  feet; 

The  strength  probably  does  not  vary  inversely  as  the  length, 
but  this  rule  is  found  to  give  sufficiently  accurate  results,  provided 
the  circular  form  is  not  departed  from  by  more  than  twice  the  thick- 
ness of  the  plates,  and  the  flue  is  not  abnormally  long. 

For  the  sake  of  simplicity  it  is  customary  to  use  t2,  rather  than 
t2'19.  As  in  all  boiler  work  t  is  a  fraction,  the  use  of  t2  will  give  a 
slightly  higher  collapsing  pressure,  which  is  provided  against  by  the 
use  of  the  larger  factor  of  safety  always  adopted  for  flues, 

The  heat  is  always  greater  on  the  top  than  on  the  bottom  of  any 
furnace-flue,  and  the  effect  of  expansion  is  to  make  the  flue  ellip- 
soidal or  egg  shaped  in  section.  The  external  pressure  on  the  flat- 
tened sides  tends  to  increase  this  distortion,  and  the  resistance  is 
found  to  be  inversely  as  the  largest  radius  of  curvature.  Similarly, 
in  flues  that  are  made  elliptical  in  section  the  above  formula  may 
be  used  by  substituting  for  d  the  diameter  of  the  larger  circle  of 

2x2 
curvature,  or  by  making  d  equal  — ,  in  which  x  and  y  are  respec- 

*  y 

tively  the  major  and  minor  axes  of  the  ellipse. 

Owing  to  the  high  pressures  now  so  general,  elliptical  flues  cannot 
be  recommended,  and  ought  not  to  be  used  except  in  special  cases. 

The  simplest  flues  are  made  of  sheets  rolled  into  proper  form,  and 
the  edges  lap  welded,  lapped  and  riveted,  or  butted  and  joined  by 
straps.  The  latter  method  is  not  popular,  due  to  the  large  area  of 
double  thickness  of  metal.  Riveted  flues  are  cheaper  than  welded 
ones.  When  flues  are  less  than  seven  inches  in  inside  diameter, 
they  are  very  difficult  to  rivet  to  the  flange  on  the  end  plate,  unless 
the  rivets  can  be  driven  from  the  outside  of  flue,  which  is  seldom 
the  case  on  account  of  the  proximity  of  the  shell  or  other  flues. 

When  long,  flues  must  be  built  up  with  successive  courses  of 
plates.  The  ring  seams  when  lapped  increase  the  strength,  and, 
within  moderate  limits,  the  length  in  the  formula  may  be  taken  as 
the  length  between  such  ring  seams.  The  successive  courses  should 
never  be  arranged  with  the  longitudinal  seams  in  line,  but  such  seams 
should  be  made  to  break  continuity  as  far  as  possible.  However, 
the  pitch  of  four  rivet  spaces  will  suffice. 


172  STEAM-BOILERS 

In  flues  of  large  diameter  and  great  length  it  would  be  neces- 
sary to  use  very  thick  metal.  In  order  to  keep  the  metal  thin,  the 
flue  must  be  strengthened  at  intervals,  so  that  the  length  may  be 
taken  as  the  length  of  such  interval. 

There  are  various  ways  of  stiffening  plain  flues. 

1.  By  Lapping  the  Various  Courses  of  Plating.     This  method  is 
little  used,  due  to  the  uncertain  amount  of  additional  strength 
attributable  to  the  laps.     Except  with  large  factors  of  safety,  such 
flues  are  usually  treated  as  plain  flues. 

2.  By  Angle  or  Tee  Rings.     Such  rings  are  placed  around  the 
flue  on  the  water  side,  and  should  be  spaced  off  from  the  flue  by  at 
least  one  inch,  so  as  to  prevent  a  double  thickness  of  metal  (Figs. 
38  and  39).     The  stays  or  bolts  are  passed  through  ferrules  or  dis- 
tance pieces,  so  as  to  keep  the  ring  firmly  in  position.     Angles  are 


FIG.  38. — Flue  Strengthening  by  Angle  Ring. 

generally  preferred  to  tees ;  and  angles  3  by  2 1-  by  f  inches  are  heavy 
enough  except  for  extremely  high  pressures.  Plain  rings  may  be 
used,  riveted  together,  with  stays  passing  between  them. 

These  methods  are  not  desirable  for  furnace-flues,  due  to  the 
tendency  of  the  flue  to  expand  more  than  the  ring,  and  the  danger 
of  breaking  off  the  heads  of  the  stays.  Reference  is  made  to  failure 
of  the  furnaces  of  the  "  Bergen,"  Transactions  Am.  Soc.  M.  E.,  Vol. 
XI,  1890,  p.  423. 

There  are  no  fixed  rules  for  spacing  the  stays,  but  care  must  be 
taken  to  keep  them  close  enough  to  lend  sufficient  support.  These 
stay-rivets  should  have  a  diameter  at  least  equal  to  one  and  one-half 
times  the  thickness  of  flue,  and  be  spaced  not  over  six  inches  apart, 
centre  to  centre. 

When  flues  are  close  together  these  rings  may  be  placed  at 
varying  distances  on  adjacent  flues  so  as  not  to  come  opposite. 


BOILER  DETAILS 


173 


Care  must  also  be  taken  not  to  allow  them  to  interfere  with  con- 
vection currents,  or  to  permit  them  to  collect  sediment  or  scale. 

3.  By  Tee  Ring  Joint.     Such  rings  may  be  used  by  riveting  to 
each  leaf  the  butting  ends  of  the  flue  sheets  (Fig.  40).     The  butts 


FIG.  39. — Flue  Strengthening  by 
Tee  Ring. 


FIG.  40. — Flue  Strengthening 
by  Tee  Ring  Joint. 


should  be  spaced  apart  far  enough  to  calk  the  edge.  This  space 
must  vary  with  the  thickness,  but  for  ordinary  plates  about  one  inch 
will  suffice.  The  size  of  tee  must  be  such  that  its  thickness  equals 
that  of  plates,  and  the  web  be  three  inches  for  ordinary  pressures. 

The  objection  is  the  double  thickness  exposed  to  the  hot  gases. 

4.  By  Flanging  the  Edges.  The  edges  may  be  flanged  up  so 
as  to  lap  the  rivet,  or  one  edge  be  flanged  up  so  as  to  lap  a  course 
of  larger  diameter  (Figs.  41  and  42).  Single-riveting  is  sufficient. 


FIG.  41. — Flue  Strengthening 
by  Flanging. 


FIG.  42. — Flue  Strengthening  by 
Flanging. 


These  methods  are  seldom  used.     The  former  is  very  expensive,  as 
it  necessitates  a  flange  on  both  sheets. 

5.  By  the  Bowling  Hoop.  This  method  has  met  with  much 
success  (Fig.  43).  It  allows  a  certain  amount  of  longitudinal 
elasticity,  but  is  expensive  and  has  two  joints  in  the  fire,  together 
with  a  double  thickness  of  metal.  It  is  used  less  than  formerly, 
having  given  way  to  the  more  favored  Adamson  ring.  The  radii 
should  be  1^  inches,  and  not  less  than  2^  times  the  thickness  of 
the  plate. 


174 


STEAM-BOILERS 


6.  By  the  Adamson  Ring.  This  is  generally  considered  the 
best  joint  for  plain  furnaces,  but  is  more  expensive  than  the  angle 
or  tee  rings,  although  very  much  the  stronger.  Now  that  good 
flanging  steel  can  be  procured  easily,  it  is  not  a  difficult  joint  to 
make.  The  ends  of  the  flue  sheets  are  flanged  out  and  are  then 


FIG.  43. — Flue  Strengthening  by  the 
Bowling  Hoop. 


K 

li" 


FIG.  44. — Flue  Strengthening  by 
the  Adamson  Ring. 


riveted  together  through  a  ring  inserted  between  them  (Fig.  44). 
The  object  of  the  ring  is  not  so  much  for  strength  as  to  facilitate 
calking  the  joint  on  the  inside.  Its  thickness  may  be  equal  to  that  of 
the  sheets.  The  flanging  should  be  over  a  radius  equal  to  2J  times 
the  thickness  of  the  sheets,  so  as  to  prevent  grooving  and  permit  of 
longitudinal  expansion.  The  advantages  are  the  facility  for  making 
and  maintaining  a  tight  joint;  the  double  thickness,  being  in  the 
water  space,  cannot  be  overheated ;  while  the  steam  pressure  tends 
to  keep  the  joint  closed.  The  objection  is  the  difficulty  of  replacing 
the  flue  as  ordinarily  designed. 

7.  By  Galloway  Tubes.     These  tubes  are  built  in  the  flues  and 
are  chiefly  used  to  increase  the  heating  surface  (Fig.  45).     Some- 


FIG.  45.— Flue  Strengthening  by  Galloway  Tubes. 

times  they  are  made  as  pockets  on  the  side  of  the  flue.  They 
should  be  shaped  like  a  truncated  cone  with  the  large  end  up,  to 
facilitate  circulation  through  them,  and  should  be  staggered  so  as 


BOILER   DETAILS 


175 


to  assist  in  mixing  the  hot  gases  and  thus  promote  combustion. 
They  are  generally  about  five  or  six  inches  in  diameter  at  the  small 
end,  increasing  to  twice  that  at  the  large  end  (Figs.  19  and  20). 

Large  flues  such  as  used  in  Cornish  and  Lancashire  boilers  do 
not  rely  on  the  additional  strength  lent  by  these  tubes,  but  are  also 
strengthened  by  rings  of  some  convenient  design.  The  disadvantage 
of  these  Galloway  tubes  is  the  trouble  to  clean  and  scale  them. 

8.  Flues  are  made  of  other  forms  than  plain,  so  as  to  be  self- 
sustaining  without  the  aid  of  stiffening  rings.  There  are  many 
patented  shapes,  but  the  principal  ones  in  use  are  Fox's  Corrugated 


FIG.  46. — Fox's  Corrugated  Furnace  Flue. 

(Fig.  46),  Morison's  Suspension  (Fig.  47),  and  Purves'  Ribbed 
Flues  (Fig.  48).  These  special  flues  are  purchased  from  the  makers, 
and  can  be  obtained  in  various  standard  diameters,  but  at  lengths 
to  suit  each  order,  and  with  either  or  both  ends  flanged  as  wanted. 
The  illustrated  catalogues  of  the  makers  should  be  consulted  with 


FIG.  47. — Morison's  Suspension  Furnace  Flue. 

respect  to  the  various  forms  of  flanging.    Usually  the  flue  ends  are 
plain,  and  are  single-riveted  to  flanges  formed  on  the  front  head  and 


176  STEAM-BOILERS 

on  the  combustion-chamber.  It  is  often  convenient  to  make  the  front 
end  of  the  flue  J  or  f  of  an  inch  larger  in  outside  diameter  than  the 
corrugations  of  the  flue,  so  as  to  facilitate  removal.  The  back  end  of 
the  flue  may  be  flanged  to  meet  the  combustion-chamber,  and  when  so 
made  it  has  the  advantage  of  placing  the  rivet-heads  out  of  the  direct 
play  of  the  flames,  and  in  consequence  will  be  more  durable.  This 


FIG.  48. — Purves'  Ribbed  Furnace  Flue. 

flange  on  the  back  end  of  the  flue  can  be  so  shaped  by  the  makers  as 
to  pass  out  through  the  hole  in  the  front  head.  All  these  forms  are 
good,  and  the  disadvantage  is  the  trouble  to  break  off  the  scale  from 
the  corrugations.  The  flatter,  therefore,  the  depressions,  the 
greater  will  be  the  ease  of  cleaning,  and  the  less  the  resistance  offered 
to  the  passage  of  the  gases.  While  the  ribbed  flues  excel  in  this 
particular,  they  have  the  disadvantage  of  unequal  thickness  of 
metal  at  the  ribs. 

Reference  is  made  to  an  article  on  "  Marine  Boiler  Furnaces," 
by  D.  B.  Morison,  Gassier  s  Magazine,  August,  1897.  This  article 
also  gives  the  results  of  the  experiments  made  by  Otto  Knaudt,  of 
the  firm  of  Schultz,  Knaudt  &  Co.,  Essen,  Germany,  on  the  elasticity 
of  form  of  furnace-flues. 

Furnace-flues  should  not  be  tapped  for  the  fastenings  of  bridge 
wall  and  grate  bearers,  as  such  tap  bolts  are  very  hard  to  keep  tight. 
This  is  especially  true  for  forms  other  than  plain.  Tapping  is  so 
easy  that  many  builders  unfortunately  adopt  this  method. 

All  flues  subjected  to  the  direct  heat  of  the  fire  should  be 
designed  so  as  to  be  as  thin  as  possible.  Many  place  the 
maximum  thickness  at  J-inch,  but  TV  or  f-inch  would  be  a  better 
limit.  Thick  flues  burn  away  very  rapidly,  until  a  thickness  of 


BOILER  DETAILS 


177 


about  TV  is  reached.  Furthermore,  thick  furnaces  are  apt  to  become 
heated  above  the  temperature  at  which  the  steel  begins  to  lose  in 
resisting  strength. 

The  liners  of  steam-chimneys  are  flues  and  subject  to  the  same 
arguments  as  stated  above,  except  that  they  may  be  made  thicker, 
because  the  gases  have  lost  much  of  their  heat  before  reaching  them. 
Liners  being  superheating  surfaces,  should  be  proportioned  with 
a  larger  factor  of  safety  than  that  used  for  flues  which  are  water- 
heating  surfaces.  They  must  not  be  made  so  thick  as  to  be  liable 
to  burn. 

Rules  for  Flues. 
1.  U.  S.  Board  of  Supervising  Inspectors  of  Steam-vessels. 

TUBES. 

Lap-welded  tubes,  used  in  boilers  whose  construction  was  commenced 
after  June  30,  1905,  having  a  thickness  of  material  according  to  their  re- 
spective diameters,  shall  be  allowed  a  working  pressure  as  prescribed  in 
the  following  table,  provided  they  are  deemed  safe  by  the  inspectors: 


Outside 
diameter. 

Thickness 
of  material. 

Greatest 
length 
allowable. 

Maximum 
pressure 
allowable. 

Inches. 

Inch. 

Feet. 

Pounds. 

1 
U 

.072 

.072 

Any  length 
do. 

225 
225 

.083 

do. 

225 

If 

.095 

do. 

225 

2 

.095 

do. 

225 

2| 

.095 

do. 

225 

4 

.109 

uO 

225 

2f 

.109 

do. 

225 

3 

.109 

do. 

225 

$i 

.120 

do. 

225 

3| 

.120 

do. 

225 

3| 

.120 

do. 

225 

4 

.134 

do. 

225 

4il- 

,  .134 

do. 

225 

5" 

.148 

do. 

225 

6 

.165 

do. 

225 

J 

FLUES. 

The  annexed  table  shall  include  all  such  riveted  and  lap-welded  flues 
exceeding  6  inches  in  diameter  and  not  exceeding  40  inches  in  diameter 
not  otherwise  provided  for  by  law. 


178 


STEAM-BOILERS 


O  H 

^  O 

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<  CO 


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s-§ 


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°^S  = 


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o  o.J 
P-I 


>  co  ooeo  ooeo 
•  i00oi-o5ooo5 


.J3    I    C  cp  u     • 

3  j?  c  : 
00,03   . 


:§&^SSg; 


OrffcJJIM  :  I: 


lllHl^  : 
>^|    |B,8  : 


O, 
t- 


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BOILER  DETAILS 


179 


§£i3 
SftS 


• 


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ml 

o  o.cc  • 


- 


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fes 


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ii 


illJti 


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180  STEAM-BOILERS 

For  any  such  flue  requiring  more  pressure  than  is  given  in  table,  the 
same  will  be  determined  by  proportion  of  thickness  to  any  given  pressure 
in  table  to  thickness  for  pressure  required,  as  per  example: 

A  flue  not  over  19  inches  in  diameter  and  3  feet  long  requires  a  thick- 
ness of  .39  of  an  inch  for  164  pounds  pressure;  what  thickness  would  be 
required  for  250  pounds  pressure  ? 

164  :  250  ::  .39  :  .5946, 

or  a  thickness  of  .595  inch. 

Or,  if  .39  inch  thickness  gives  a  pressure  of  164  pounds,  what  will  .595 
inch  thickness  give  ? 

.39  :  .595  ::  164  :  250  pounds  required. 

And  all  such  flues  shall  be  made  in  sections,  according  to  their  respect- 
ive diameters,  not  to  exceed  the  lengths  prescribed  in  the  table,  and  such 
sections  shall  be  properly  fitted  one  into  the  other  and  substantially  riveted, 
and  the  thickness  of  material  required  for  any  such  flue  of  a  given  diameter 
shall  in  no  case  be  less  than  the  least  thickness  prescribed  in  the  table  for 
any  such  given  diameter;  and  all  such  flues  may  be  allowed  the  prescribed 
working  steam  pressure  if,  in  the  opinion  of  the  inspectors,  it  is  deemed 
safe  to  make  such  allowance.  Inspectors  are  therefore  required,  from 
actual  measurement  of  each  flue,  to  make  such  reduction  from  the  pre- 
scribed working  steam  pressure  for  any  material  deviation  in  the  uniform- 
ity of  the  thickness  of  material,  or  from  any  material  deviation  in  the  form 
of  the  flue  from  that  of  a  true  circle,  as  in  their  judgment  the  safety  of 
navigation  may  require. 

FURNACES. 

The  tensile  strength  of  steel  used  in  constructing  furnaces  shall  not 
exceed  67,000,  and  be  not  less  than  58,000  pounds.  The  minimum  elonga- 
tion in  8  inches  shall  be  20  per  cent. 

All  corrugated  furnaces  having  plain  parts  at  the  ends  not  exceeding  9 
inches  in  length  (except  flues  especially  provided  for),  when  new,  and  made 
to  practically  true  circles,  shall  be  allowed  a  steain  pressure  in  accordance 
with  the  following  formula: 


BOILER  DETAILS  181 

LEEDS   SUSPENSION   BULB   FURNACE. 

CXT7 

D 
where  P  =  pressure  in  pounds  ; 

T  =  thickness  in  inches,  not  less  than  five-sixteenths  of  an  inch  ; 
D  =.  mean  diameter  in  inches  ; 

(7=a  constant,  17,300,  determined  from  an  actual  destructive  test 
under  the  supervision  of  the  Board,  when  corrugations  are 
not  more  than  8  inches  from  center  to  center,  and  not  less 
than  2J  inches  deep. 

MORISON   CORRUGATED   TYPE. 

CxT 


D 

where  P  =  pressure  in  pounds  ; 

2T=thickness  in  inches,  not  less  than  five-sixteenths  of  an  inch  ; 

D  =mean  diameter  in  inches  ; 

C  =-15, 600,  a  constant,  determined  from  an  actual  destructive  test 
under  the  supervision  of  the  Board  of  Supervising  Inspectors, 
when  corrugations  are  not  more  than  8  inches  from  center  to 
center,  and  the  radius  of  the  outer  corrugations  is  not  more 
than  one-half  of  the  suspension  curve. 

[In  calculating  the  mean  diameter  of  the  Morison  furnace,  the  least  in- 
side diameter  plus  2  inches  may  be  taken  as  the  mean  diameter,  thus  : 

Mean  diameter  =least  inside  diameter  +  2  inches.] 

FOX  TYPE. 

p__CxT 
D 

where  P=pressure  in  pounds  ; 

T=thickness  in  inches,  not  less  than  five-sixteenths  ; 
Z)  =  mean  diameter  in  inches  ; 

C  —  14,000,  a  constant,  when  corrugations  are  not  more  than  8  inches 
from  center  to  center  and  not  less  than  1£  inches  deep. 

PURVES  TYPE. 


D 


182  STEAM-BOILERS 

where  P=  pressure  in  pounds  ; 

T=  thickness  in  inches,  not  less  than  seven-sixteenths  ; 
D  =  least  outside  diameter  in  inches  ; 

C=  14,000,  a  constant,  when  rib  projections  are  not  more  than  9 
inches  from  center  to  center  aud  not  less  than  If  inches 
deep. 

The  thickness  of  corrugated  and  ribbed  furnaces  shall  be  ascertained 
by  actual  measurement.  The  manufacturer  shall  have  said  furnace  drilled 
for  a  one-fourth  inch  pipe  tap  and  fitted  with  a  screw  plug  that  can  be  re- 
moved by  the  inspector  when  taking  this  measurement.  For  the  Brown 
and  Purves  furnaces  the  holes  shall  be  in  the  center  of  the  second  flat ;  for 
the  Morison,  Fox,  and  other  similar  types  in  the  center  of  the  top  corruga- 
tion, at  least  as  far  in  as  the  fourth  corrugMtion  from  the  end  of  the  fur- 
nace. 

TYPE   HAVING   SECTIONS    18    INCHES   LONG. 

CXT 
D 

where  P=  pressure  in  pounds  ; 

T=  thickness  in  inches,  not  less  than  seven-sixteenths  ; 

D  =  mean  diameter  in  inches  ; 

(7=  10,000,  a  constant,  when  corrugated  by  sections  not  more  than 
18  inches  from  center  to  center  and  not  less  than  2£  inches 
deep,  measuring  from  the  least  inside  to  the  greatest  outside 
diameter  of  the  corrugations,  and  having  the  ends  fitted  one 
into  the  other  and  substantially  riveted  together,  provided 
that  the  plain  parts  at  the  ends  do  not  exceed  12  inches  in 
length. 

ADAMSON   TYPE. 

When  plain  horizontal  flues  are  made  in  sections  not  less  than  18  inches 
in  length,  and  not  less  than  five-sixteenths  of  an  inch  thick,  and  flanged  to 
a  depth  of  not  less  than  three  times  the  diameter  of  rivet-hole  plus 
the  radius  at  furnace  wall  (inside  diameter  of  furnace),  the  thickness 
of  the  flanges  to  be  as  near  the  thickness  of  the  body  of  the  plate  as 
practicable. 

The  radii  of  the  flanges  on  the  fire  side  shall  be  not  less  than  three 
times  the  thickness  of  plate. 

The  distance  from  the  edge  of  the  rivet-hole  to  the  edge  of  the  flange 
shall  be  not  less  than  the  diameter  of  the  rivet-hole,  and  the  diameter  of 
the  rivets  before  driven  shall  be  at  least  one-fourth  inch  larger  than  the 
thickness  of  the  plate. 


BOILER  TETAILS  183 

The  depth  of  the  ring  between  the  flanges  shall  be  not  less  than  three 
times  the  diameter  of  the  rivet-holes,  and  the  ring  shall  be  substantially 
riveted  to  the  flanges.  The  fire  edge  of  the  ring  shall  terminate  at  or  about 
the  point  of  tangency  to  the  curve  of  the  flange,  and  the  thickness  of  the 
ring  shall  be  not  less  than  one-half  inch. 

The  pressure  allowed  shall  be  determined  by  the  following  formula  : 

PLAIN   CIRCULAR   FURNACES   OR   FLUES,    AND    ADAMSON   FURNACES   MADE   IN 
SECTIONS   NOT   LESS   THAN    18    INCHES    IN   LENGTH. 

P  =^[18.75r  -  (L  X  1.03)] 

where  P=  working  pressure  in  pounds  per  square  inch  ; 
J)= outside  diameter  of  furnace  in  inches  ; 
i=length  of  furnace  in  inches  ; 
T=  thickness  of  plate  in  sixteenths  of  an  inch. 

VERTICAL   TYPE. 

Cylindrical  flues  used  as  furnaces  in  vertical  boilers,  when  new,  and 
made  to  practically  true  circles,  shall  be  allowed  a  steam  pressure  by  the 
following  formula  :j 

CXT 
D 

where  P=  pressure  of  steam  allowable  in  pounds  ; 

T=thickness  of  flue  in  inches,  not  less  than  one-fourth  ; 

D  =  outside  diameter  of  flue  in  inches,  not  to  exceed  42  inches  ; 

(7=10,577,  a  constant,  when  the  length  of  the  flue  does  not  exceed 
42  inches,  measuring  from  the  center  of  the  rivet-holes  in  the 
head  to  the  center  of  the  rivet-holes  in  the  leg. 

"When  the  flue  exceeds  42  inches  in  diameter,  it  is  deemed  to  be  flat  sur- 
face and  must  be  stayed  accordingly. 

STEAM-CHIMNEY  FLUES. 

The  Morison,  Fox,  Purves,  or  Brown  types  of  corrugated  furnaces  may 
be  used  as  flues  for  steam  chimneys  or  superheaters  and  shall  be  allowed  a 
steam  pressure  by  their  respective  formula?,  and  other  flues,  as  described 
below,  when  new  and  made  to  practically  true  circles,  shall  be  allowed  a 
steam  pressure  by  the  following  formula: 


184  STEAM-BOILERS 

where  P=  pressure  in  pounds  ; 

T=thickness  of  material  in  inches  ; 
D=outside  diameter  of  flue  in  inches  ; 

(7=12,000  for  flues  under  30  inches  in  diameter,  plates  at  least  five- 
sixteenths  of  an  inch  thick,  supported  by  angle  rings  at  least 

2£  by  2i  inches  ; 
(7=12,000  for  flues   30  inches  and  under  45  inches  in  diameter, 

plates  at  least  three-eighths  of  an  inch  thick,  supported  by 

angle  rings  at  least  2i  by  2|  inches  ; 
(7=12,000  for  flues  45  inches  and  under  55  inches  in  diameter,  plates 

at  least  seven-sixteenths  of  an  inch  thick,  supported  by  angle 

rings  at  least  3  by  3  inches  ; 
(7=12,000  for  flues  55  inches  and  under  65  inches  in  diameter,  plates 

at  least  one-half  inch  thick,  supported  by  angle  rings  at  least 

3  by  3  inches ; 

(7=12,000  for  flues  65  inches  and  under  75  inches  in  diameter,  plates 
at  least  nine-sixteenths  of  an  inch  thick,  supported  by  angle 
rings  at  least  3i  by  3|  inches. 

C=  12,000  for  flues  75  inches  and  under  85  inches  in  diameter,  plates 
at  least  five-eighths  of  an  inch  thick,  supported  by  angle  rings 
at  least  3£  by  3i  inches. 

(7=12,000  for  flues  85  inches  in  diameter,  plates  at  least  eleven- 
sixteenths  of  an  inch  thick,  supported  by  angle  rings  at  least 

4  by  4  inches. 

For  flues  over  85  inches  in  diameter,  add  one-sixteenth  of  an  inch  to 
eleven-sixteenths  of  an  inch  for  every  10  inches  increase  in  the  diameter 
of  the  flue. 

The  distance,  center  to  center,  between  angle  rings,  or  center  of  angle 
rings  to  center  of  rivets  in  the  heads,  shall  in  no  case  exceed  2|  feet. 

The  angle  rings  shall  be  accurately  fitted  and  substantially  riveted  to 
the  flue  and  connected  to  the  outer  shell  by  braces,  which  braces  shall  not 
exceed  20  inches  from  center  to  center  on  the  flue. 

2.  Board  of  Trade  (British). 
The  working  pressure  in  pounds  per  square  inch  is 

Constant  x  square  of  thickness  of  plate  in  inches 
(Length  in  feet-f  1)  x  diameter  in  inches        ' 

9000  x  thickness  in  inches 
provided  that   the  pressure  does   not  exceed  .     diameter  in  lncheg 


BOILER  DETAILS 


185 


Value  of  Constants: 
90,000 


Furnaces 
with  butt- 
joints  and 
drilled 
rivet-holes. 


Furnaces 
with  butt- 
joints  and 
punched 
rivet-holes. 


Furnaces 
with  lapped 
joints  and 
drilled 
rivet-holes. 


Furnaces 
with  lapped 
joints  and 
punched 
rivet-holes. 


90,000 
80,000 
90,000 


85,000 
75,000 
85,000 


where  the  longitudinal  seams  are  welded, 
where  the  longitudinal  seams  are  double-riveted 
and  fitted  with  single  butt-straps, 
where  the  longitudinal  seams  are   single-riveted 
and  fitted  with  single  butt-straps, 
where  the  longitudinal  seams  are  single-riveted 
and  fitted  with  double  butt-straps, 
where  the  longitudinal  seams  are  double-riveted 
and  fitted  with  single  butt-straps, 
where  the  longitudinal  seams  are   single-riveted 
and  fitted  with  single  butt-straps, 
where  the  longitudinal  seams  are  single-riveted 
and  fitted  with  double  butt-straps. 


I 

80,000  where  the  longitudinal  seams  are  double-riveted 

and  bevelled. 
75,000  where  the  longitudinal  seams  are  double-riveted 

and  not  bevelled. 
70,000  where  the  longitudinal  seams  are  single-riveted 

and  bevelled. 
65,000  where  the  longitudinal  seams  are  single-riveted 

and  not  bevelled. 

75,000  where  the  longitudinal  seams  are  double-riveted 

and  bevelled. 
70,000  where  the  longitudinal  seams  are  double-riveted 

and  not  bevelled. 
65,000  where  the  longitudinal  seams  are  single-riveted 

and  bevelled. 
60,000  where  the  longitudinal  seams  are  single-riveted 

and  not  bevelled. 


The  above  constants  are  for  use  when  flues  are  made  of  iron;  but 
when  of  steel,  increase  the  constants  10  per  cent.  The  length  is  to  be 
measured  between  the  rings  if  the  furnace  is  made  with  rings. 

When  furnaces  are  machine-made,  of  the  Fox  corrugated,  the  Mori- 
son  suspension,  or  the  Purves  ribbed  types,  and  the  plates  are  not  less 
than  &  inch  thick,  the  working  pressure  per  square  inch 

__  14,000  X  thickness  in  inches 
Outside  diameter  in  inches' 

The  diameter  is  measured  at  the  bottom  of  the  corrugations  or  over 
the  plain  part  between  ribs. 


186  STEAM-BOILERS 

When  furnaces  of  ordinary  diameter  are  constructed  of  a  series  of 
rings  welded  longitudinally,  and  the  ends  of  each  ring  flanged  and  the 
rings  riveted  together,  and  so  forming  the  furnace,  the  working  pressure 
is  found  by  the  following  formula,  provided  the  length  in  inches  between 
the  centres  of  the  flanges  of  the  rings  is  not  greater  than  (120£  —  12),  and 
the  flanging  is  performed  at  one  heat  by  machine: 

9900X*/        Z  +  12\ 
\ 


in  which  t  denotes  thickness  of  plate  in  inches; 

I        "      length  between  centre  of  flanges  in  inches; 
d       "      outside  diameter  of  furnace  in  inches. 

The  radii  of  the  flanges  on  the  fire  side  should  be  about  1^  inches. 
The  depth  of  the  flanges  from  fire  side  should  be  three  times  the  diam- 
eter of  the  rivet  plus  1^  inches,  and  the  thickness  of  the  flanges  should 
be  as  near  the  thickness  of  body  of  plates  as  practicable.  The  distance 
from  edge  of  rivet  holes  to  edge  of  flange  should  not  be  less  than  diameter 
of  rivet,  and  the  diameter  of  rivet  at  least  f  inch  greater  than  the  thick- 
ness of  plate.  The  depth  of  ring  between  flanges  should  be  not  less 
than  three  times  the  diameter  of  rivet,  the  fire  edge  of  ring  should  be 
at  about  the  termination  of  the  curve  of  flange,  and  the  thickness  not 
less  than  half  the  thickness  of  the  furnace  plate.  It  is  very  desirable 
that  these  rings  should  be  turned.  After  all  welding,  flanging  and  heating 
is  completed  each  ring  should  be  efficiently  annealed  in  one  operation. 

Tubes.  In  fire-tubular  boilers,  the  number  of  tubes  and  the 
size  required  depend  on  the  area  through  them  for  purposes  of 
draft  and  on  the  amount  of  heating  surface  necessary  to  absorb 
the  heat  of  the  fire.  The  area  for  draft  has  been  discussed  in  a 
previous  chapter. 

With  regard  to  heating  surface,  it  must  be  remembered  that 
increasing  the  diameter  increases  the  surface  in  direct  proportion 
and  the  calorimeter  in  proportion  to  the  square  of  the  diameters. 
The  size  needed  to  suit  both  calorimeter  and  heating  surface  can  be 
determined  by  trial  until  one  size  is  found  which  will  give  a  result 
nearest  to  that  wanted. 

The  size  is  also  generally  dependent  on  the  quality  of  fuel  to  be 
used.  With  hard  coals,  tubes  3  inches  and  less  in  diameter  are 
used;  while  with  soft  coals,  3  inches  and  over  are  preferred,  as 
smaller  tubes  choke  up  too  rapidly  with  soot. 


BOILER   DETAILS  187 

It  is  not  advisable  to  make  tubes  more  than  50  or  60  diameters 
in  length,  as  the  additional  length  loses  rapidly  in  evaporating 
efficiency.  Instead  of  increasing  the  length,  it  is  better  to  use  more 
tubes  of  smaller  diameter,  even  though  the  proposed  calorimeter 
cannot  be  obtained,  provided,  of  course,  that  too  small  a  calorimeter 
is  not  used  so  as  to  restrict  the  draft. 

In  large  boilers  it  is  best  to  arrange  the  tubes  in  banks  or  nests, 
by  leaving  out  the  vertical  middle  row.  This  wide  water  space 
assists  the  convection  currents  and,  therefore,  the  evaporative 
power  of  the  boiler.  In  Scotch  boilers,  the  tubes  always  should  be 
thus  divided  into  nests. 

The  outer  rows  also  should  be  kept  far  enough  away  from  the 
shell,  so  as  not  to  interfere  with  the  downward  currents ;  but  since 
the  tubes  act  as  stays  they  must  not  be  placed  too  far  from  the 
shell,  or  the  tube  plates  will  have  to  be  made  too  thick.  In  horizon- 
tal return-tubular  and  similar  boilers  the  distance  between  outer 
tubes  and  shell  should  not  be  less  than  3  inches,  and  when  the  boilers 
exceed  50  inches  diameter  it  should  be  more. 

The  tubes  should  be  arranged  in  horizontal  and  vertical  rows, 
so  that  the  steam  bubbles  can  have  a  direct  passage  through  the 
vertical  spaces  to  the  surface,  and  not  be  staggered  except  in 
locomotives.  The  pitch  of  the  tubes  horizontally  should  never 
be  less  than  that  of  the  vertical  rows.  When  the  pitch  vertically 
is  small,  then  the  horizontal  pitch  should  be  greater  by  at  least 
an  eighth  to  a  quarter  inch. 

The  pitch  ought  not  to  be  less  than  1.4  times  the  diameter  under 
ordinary  conditions,  but  if  care  be  taken  in  the  general  design,  and 
the  tubes  are  not  over  30  diameters  in  length,  they  can  be  spaced 
nearer  together.  Three-inch  and  smaller  tubes  could  be  spaced 
so  as  to  leave  only  }  inch  between  holes  in  tube  plates,  but  such 
small  pitch  is  too  close  for  good  steaming  purposes.  The  distance 
between  such  tubes,  if  possible,  ought  not  to  be  less  than  1  inch 
vertically  and  1 J-  inch  horizontally.  If  proper  spacing  be  neg- 
lected, priming  is  apt  to  occur  when  the  boiler  is  forced. 

The  top  row  of  tubes  should  be  placed  low  enough  so  as  to 
leave  ample  steam  space  and  permit  some  of  the  water  surface 
to  extend  over  the  spaces  left  for  downward  currents  at  the  sides, 
between  the  tubes  and  the  shell.  As  a  general  thing  it  is  diffi- 
cult to  get  the  tubes  low  enough. 

In  large  shell  boilers,  like  the  Scotch,  the  top  row  should  not  be 


188  STEAM-BOILERS 

higher  than  one-third  the  diameter  of  shell  from  the  top,  but  may  be 
0.28  of  the  diameter  when  the  outflow  of  steam  is  very  regular,  as 
for  marine  engines  of  comparatively  short  stroke.  In  horizontal 
return-tubular  boilers  the  uppermost  row  is  generally  about  two- 
fifths  of  shell  diameter  from  top. 

The  best  method  is  to  make  preliminary  sketches,  to  scale,  of  the 
proposed  cross-section,  and  locate  by  trial  and  error  the  positions 
of  tubes,  flues,  stays  and  other  internal  arrangements. 

Provided  that  the  total  area  of  tube  opening  be  neither  too  large 
nor  too  small,  the  economy  appears  to  be  little  affected  by  the  size 
of  the  tube  employed.  Still,  as  small  tubes  become  more  rapidly 
choked  with  soot  than  large  ones,  the  latter  had  better  be  used  with 
soft  coals  and  wood,  unless  the  conditions  are  such  as  to  permit 
frequent  cleaning.  Tube  diameters  are  always  given  on  outside 
measurement,  so  that  the  area  of  opening  corresponds  to  a  diameter 
equal  to  that  of  tube  less  twice  the  thickness. 

The  tubes  act  as  stays  in  supporting  the  tube  plates.  In  large 
boilers  with  high  steam  pressures,  some  of  the  ordinary  tubes  are 
replaced  with  extra  heavy  tubes,  called  "stay  tubes."  The  use  of 
these  stay  tubes  is  more  common  in  European  practice  than  in  this 
country,  and  more  common  in  marine  than  in  stationary  boilers. 
When  used,  every  fourth  tube  is  generally  made  a  stay  tube. 

Boiler  tubes  are  made  of  solid  drawn  brass,  and  of  lap-welded 
iron  or  steel.  Steel  tubes  can  also  be  made  solid  drawn.  Brass 
tubes  are  little  used  at  present,  preference  being  given  to  charcoal 
iron  or  to  mild  steel.  Steel  tubes  are  said  to  be  less  durable  than 
iron  tubes,  but  the  fault  is  chiefly  in  the  poor  quality  of  steel  fur- 
nished. The  best  steel  should  be  just  as  able  to  withstand  wear  and 
corrosion  as  the  best  iron.  Poor  qualities  are  more  difficult  to 
detect  by  visual  inspection  in  steel  than  in  iron,  and  for  cheap  work 
iron  tubes,  therefore,  are  preferred  by  many. 

Nickel-steel  has  been  used  to  some  extent  for  boiler-tubes,  and 
the  result  so  far  has  been  favorable.  A.  F.  Yarrow  *  made  some 
experiments  on  nickel  versus  mild  steel  for  water  tubes  with  the 
following  results:  The  nickel  alloy  contained  from  20  per  cent  to 
25  per  cent  of  nickel.  Boiler  tubes  deteriorate  from  three  principal 
causes,  (a)  action  of  acids,  due  to  grease;  (b)  overheating  and 

*  Inst.  of  Naval  Architects,  July,  1899,  and  Journal  American  Society 
Naval  Engineers,  August,  1899. 


BOILER  DETAILS 


189 


oxidizing  through  contact  with  hot  gases;  (c)  action  of  superheated 
steam,  which  decomposes. 

The  corrosion  tests  showed  that  mild  steel  lost  sixteen  and  a  half 
times  more  weight  than  nickel-steel,  and  the  oxidization  tests  two 
and  nine-tenths  times.  The  superheated  steam  tests  showed  a  loss 
in  nickel-steel  of  12.7  grammes  against  85.2  grammes  in  mild  steel, 
or  that  mild  steel  tubes  would  have  to  be  replaced  two  and  one- 
third  times  as  often  as  nickel-steel  ones.  The  expansion  test  showed 
that  nickel-steel  expands  more  than  mild  steel  in  the  ratio  of  four  to 
three.  Small  amounts  of  nickel,  about  five  per  cent,  produced  only 
slight  gains. 

TABLE  XVII 

THE   GREATEST   NUMBER    OF  TUBES   USUALLY   PLACED    IN    HORIZONTAL   RETURN 

TUBULAR    BOILERS 


Diameter  of 
Boiler-Shell 
in  Inches. 

Diameter  of  Tubes. 

3  Inches. 

3i  Inches. 

4  Inches. 

30 

20 

14 

10 

36 

32 

22 

16 

42 

45 

32 

25 

44 

48 

33 

26 

48 

56 

38 

27 

50 

60 

40 

30 

54 

70 

48 

36 

60 

84 

62 

48 

62 

90 

70 

52 

64 

96 

78 

58 

66 

104 

86 

64 

72 

126 

98 

78 

78 

160 

124 

100 

The  holes  in  the  tube  plates  should  be  drilled  to  a  perfect  fit, 
and  the  burr  should  be  removed  with  light  filing.  The  tubes  should 
be  cut  to  proper  length  and  fitted  into  place.  The  tube  makers  will 
supply  the  tubes  of  the  desired  length,  as  well  as  slightly  upsetting 
one  end  to  TV  larger  diameter.  This  enlargement  of  the  end  facili- 
tates the  tube's  removal  at  any  time,  but  is  a  refinement  seldom 
adopted,  except  for  stay  tubes  or  for  tubes  screwed  into  tube  sheets. 

Plain  tubes  are  fastened  to  the  tube  sheets  by  expanding  the 
ends.  This  is  done  by  a  special  tool  called  a  "tube  expander," 
which  operates  by  simply  stretching  the  metal  so  as  to  closely  fit 
the  hole.  If  a  tube  leaks  at  the  joint,  it  may  be  expanded  again. 


190 


STEAM-BOILERS 


There  are  two  forms  of  expanders  in  common  use:  The  Prosser 
expander  (Fig.  49)  consisting  of  a  tapered  mandril  carrying  segments 


FIG.  49. — Prosser's  Tube  Expander. 

with  radial    joints,  and    operated    by  repeatedly  driving   in   the 
mandril,  slightly  turning  the  segments  at  each  operation;   and  the 


FIG.  50. — Dudgeon's  Tube  Expander. 

Dudgeon  expander  (Fig.  50)  consisting  of  a  tapered  mandrel  carry- 
ing a  hollow  steel  head  with  rollers,  and  operated  by  turning  the 


FIG.  51. — Effect  of  Expanding  the  Tube  Ends.     a.   Expanded  by  Dudgeon's 
expander  and  flared,     b.  Expanded  by  Prosser's  expander  and  beaded. 

mandrel  while  it  is  gently  forced  in,  thus  rolling  the  tube  metal  out 
into  a  tight  fit.  The  effect  of  expanding  the  tube  ends  is  shown 
in  Fig.  51. 

Of  the  two  types,  the  latter  is  less  apt  to  cause  injury  to  the  tube 


BOILER   DETAILS 


191 


end  or  to  distort  the  tube-sheet  when  used  by  inexperienced  men, 
and  is  much  liked  on  account  of  its  rolling  action  and  the  ease  with 
which  it  can  be  adjusted  to  suit  varying  thickness  of  tube-sheets. 

Tubes  exceeding  5  inches  in  diameter  cannot  be  expanded  so  as 
to  form  a  permanent  tight  joint,  as  the  metal  stretches  away  at  one 
place  while  being  pressed  tight  at  another. 

The  projecting  tube  ends  may  be  beaded  over — that  is,  rolled 
back  outwardly  so  as  to  cover  the  joint  (Fig.  516).  This  makes  a 
very  neat  appearance  when  well  done,  and  is  the  common  American 
practice.  Only  tubes  of  good,  soft  material  will  bead  smoothly, 
and  tubes  that  show  fraying  at  the  ^ 

bead  had  better  be  cut  out  and 
replaced.  Probably  as  good  a 
practice  as  any  is,  after  expanding, 
to  bead  the  tube  at  the  fire-enter- 
ing end,  and  to  drive  a  slightly 
tapered  plug  into  the  fire-exit  end, 
so  as  to  make  it  slightly  flared 
(Fig.  5 la).  Afterwards  these  ends 
should  be  all  milled  off  evenly 
and  'not  leave  over  T3g--inch  to  pro- 
ject beyond  the  tube-sheet. 

Some  engineers  prefer  to  make 
the  hole  in  the  tube-sheet  tapered, 
to  increase  the, holding  power  of 
the  tube.  If  so  made,  the  inner 
sharp  edge  must  be  slightly 
rounded.  The  holding  power  of 
expanded  tubes,  even  if  not 
beaded  or  wedged  out  like  a  cone, 
has  proved  to  be  ample  to  sup- 
port the  tube-sheets. 

Stay-tubes  are  generally  made  £-inch  in  thickness  for  all  pres- 
sures, but  are  sometimes  made  slightly  heavier.  They -are  fastened 
by  screwing  into  the'  tube-plates,  and  sometimes  carry  nuts  on  the 
outside.  Stay-tubes  have  not  been  found  necessary  except  for  very 
heavy  pressures  and  wide  spacing.  One  end  should  be  upset  so  as  to 
easily  set  and  withdraw  them,  and  the  threads  on  both  ends  should 
be  continuous. 


FIG.  52. — Ferrules  for  Tube  Ends. 


192 


STEAM-BOILERS 


In  order  to  increase  the  holding  power,  to  pre- 
vent the  ends  from  becoming  overheated  and  from 
leaking,  many  engineers  drive  ferrules  (Fig.  52)  into 
the  tubes.  These  ferrules  are  made  of  iron  or  copper 
rings,  or  of  malleable  cast  iron  in  the  shape  of  a 
nozzle.  They  are  generally  put  in  the  fire-entering 
end,  although  many  locomotives  have  them  in  the 
front  or  exit  end.  They  often  stop  leaking  tubes  by 
keeping  the  tube  end  cool.  Leaking  tubes  are 
frequent  in  some  boilers.  The  trouble  may  be 
caused  by  expansion  through  too  stiff  a  tube-plate. 
These  tube-plates  should  be  as  thin  as  can  be  con- 
veniently made. 

Retarders  (Fig.  53)  are  often  placed  in  the 
tubes  in  order  to  more  thoroughly  mix  the  products 
of  combustion  and  to  break  up  the  "  steam  lines," 
so  that  all  hot  particles  will  come  into  contact  with 
the  tube  surface.  These  retarders  are  frequently 
of  patented  forms,  but  more  or  less  resemble  a 
spiral  or  corkscrew  shaped  piece  of  metal  set  inside 
the  tube.  They  can  be  withdrawn  for  cleaning  the 
tube,  or  replaced  when  worn  out.  They  work 
best  with  a  very  strong  natural  or  mechanical 
draft.  Tubes  with  retarders  should  be  one  size 
larger  than  those  without,  under  similar  conditions. 

Retarders  have  proved  beneficial  with  the  use 
of  fuel-oil,  as  the  products  of  combustion  are  apt 
to  pass  too  freely  through  the  tubes  of  the  boiler 
and  escape  into  the  stack,  with  the  result  that 
the  water  does  not  absorb  the  heat  from  the  oil 
vaporized  in  the  furnace.  This  difficulty  is 
especially  apparent  in  boilers  designed  for  using 
either  coal  or  oil  as  a  fuel;  and  the  cause  can  be 
attributed  to  the  fact  that  the  tubes,  when  made 
sufficiently  large  to  allow  an  accumulation  of  soot 
without  obstructing  the  draft,  have  too  great  a 
sectional  area  when  oil  is  used.  With  oil  fuel 
there  is  practically  no  soot  to  collect,  and  the  hot 
gases  rush  through  them  under  the  impetus  given 


BOILER   DETAILS 


193 


by  the  pressure  of  the  burner  and  the  strong  draft  produced  by 
the  stack. 

Luther  D.  Lovekin  has  invented  the  Acme  patent  retarder 
shown  in  Fig.  54,  made  of  refractory  clay  and  in  shape  somewhat 
like  the  Admiralty  ferrule.  These  retarders  are  inserted  at  each 
end  of  the  tubes,  causing  a  reduction  in  area,  and  consequently 
retard  the  passage  of  the  hot  gases.  The  refractory  nature  of 


FIG.  54. — Acme  Refractory  Clay  Retarder  for  use  with  Fuel  Oils. 

these  Acme  retarders  will  cause  them  to  retain  their  incandes- 
cence for  some  time  after  the  fuel  has  been  shut  off  and  will  tend 
to  reignite  the  gases  should  the  flame  become  accidentally  ex- 
tinguished by  water  getting  into  the  oil. 

The  Acme  retarders  have  been  tried  on  the  steamships  "Ligo- 
nier"  and  "Larimer"  of  the  Guffey  Petroleum  Company,  1903. 
They  produced  no  smoke  and  were  found  to  reduce  the  tempera- 
tures, when  used  with  the  Lassoe-Lovekin  air-blast  and  Rockwell 

steam-blast  pulverizers,  as  follows: 

Temperature  at 
Rase  of  Stack. 

Trial  without  any  retarders 850°  F. 

' '    with  spiral  steel  retarders 750°  ' ' 

1 '    with  spiral  steel  retarder,  and  with  Acme  retarder 

at  front  end  of  tube  only 680°  " 

(l    with  Acme  retarders  at  both  ends  of  tubes   (no 

spiral  steel  retarder) 550°  ' ' 

With  smaller  opening  in  retarders  the  temperature  could 

be  as  low  as..  450°" 


194 


STEAM-BOILERS 


The  Serve  tube  (Fig.  55)  is  a  tube  having  internal  ribs  reach- 
ing about  half-way  to  the   centre.     These  ribs  increase  the  heat 

transmitting  power  of  the  tube, 
and  effect  some  economy.  It 
is  much  stiffer  and  much  more 
durable  than  the  ordinary  tube. 
It  is  more  costly  at  first,  but 
probably,  in  many  cases, 
cheaper  in  the  end.  The  ribs 
interfere  with  cleaning  to  some 
extent.  As  some  area  is  occu- 
pied by  the  ribs,  one  size  larger 
than  plain  tubes  should  be  used 
in  order  to  obtain  the  required 

calorimeter. 
FIG.  55. — Serve   lube. 

Tubes  are  made  of  standard 

or  list  thickness,  but  can  be  ordered  of  any  thickness  as  required. 

RULES  FOR  THICKNESS  OF  BOILER-TUBES. 

1.  U.    S.  Board   of   Supervising   Inspectors    of   Steam-vessels. 
Given  under  the  rules  for  flues. 

2.  As  given  by  A.  E.  Seaton  in  "Manual  of  Marine  Engineering," 
for  minimum  thickness  in  numbers  of  Birmingham  Wire  Gauge. 


External  diameter  of  tubes  
List  or  thickness  for  40  Ibs  

2 
12 

2* 

12 

$ 

2f 

11 

3 
11 

31 
10 

3* 
10 

3f 

10 

4 
9 

Thickness  for  under  90  Ibs  . 

11 

11 

10 

10 

10 

9 

9 

9 

8 

Thickness  for  over  90  Ibs 

11 

10 

q 

q 

q 

8 

8 

8 

7 

Stays.  Parts  of  many  boilers  must  be  stayed  in  order  to  with- 
stand the  steam  pressure.  Flat  surfaces  obtain  their  resisting 
strength  from  the  stays,  and  the  thickness  of  flat  plates  is  dependent 
on  the  distance  between  stays.  There  is,  therefore,  a  choice  for 
the  designer  in  determining  for  each  case  the  proper  distance  be- 
tween stay  centres  and  the  requisite  plate  thickness,  or  vice  versa. 

The  tubes  act  as  stays,  as  has  already  been  seen,  and  give  the 
required  support  to  the  tube-sheets. 

Stays  may  be  of  round,  square  or  flat  sections,  as  most  con- 
venient. 


BOILER  DETAILS 


195 


They  may  be  passed  through  the  stayed  sheet  with  the  ends 
riveted  over,  or  screwed  into  the  sheet  with  riveted  ends,  or 
screwed  into  the  sheet  with  a  nut  or  with  a  nut  and  a  washer. 
Flat  or  square  stays  are  usually  flanged  and  forged  on  the  end  to 


FIG.  56. — Screw  Stay,  ends  upset 
and  riveted. 


FIG.  57. — Screw  Stay,  ends  upset 
and  fitted  with  nuts. 


produce  a  palm  for  riveting,  or  may  have  a  single  or  double  palm 
end  forged  on.  Sometimes  a  tee  or  angle  is  riveted  to  the  stayed 
sheet,  and  the  stay  fastened  to  such  piece  or  pieces  by  a  bolt  or 
bolts.  In  many  instances  gusset  plates  are  used  instead  of  stay- 
rods.  When  the  area  of  flat  surface  to  be  supported  is  small,  it 
often  can  be  stiffened  sufficiently  by  simply  riveting  a  tee  or  two 
angles  back  to  back. 

When  screw-stays  are  used  the  ends  should  be  " upset"  (Figs. 
56,  57,  and  61),  so  as  to  retain  the  full  strength  at  the  bottom  of  the 


FIG.  58. — Screw  Stay,  ends  not 
upset,  fitted  with  nuts  and  washers. 


FIG.  59. — Stay  fitted  with 
ferrule. 


threads.  Short  screw-stays,  such  as  are  used  to  stay  water-legs 
and  similar  places,  often  can  be  conveniently  made  by  cutting  the 
thread  on  the  full  length  and  then  turning  off  the  thread  on  the  part 


196 


STEAM-BOILERS 


between  the  sheets.  This  will  leave  the  twist  of  the  thread  con- 
tinuous and  facilitate  its  insertion.  A  smooth  surface  is  better  able 
to  withstand  corrosion,  which  is  very  liable  to  attack  the  metal  at 
the  base  of  the  thread. 

Small  screw-stays  and  stay-bolts  can  be  fastened  by  riveting 
over  the  ends  of  the  stays  (Figs.  56  and  59),  but  this  method  should 
not  be  adopted  when  the  thickness  of  sheet  is  less  than  half  the 
diameter  of  stay.  In  such  cases  it  is  best  to  fasten  with  a  nut  on 
the  outside  end  of  stay.  (Figs.  57  and  58.) 

Stays  that  screw  into  the  sheet  make  a  tighter  and  more  durable 
joint  than  those  which  are  simply  passed  through  a  plain  hole. 
Screw-stays  always  should  be  used  in  high-pressure  boilers.  Screw 
stay-bolts  may  be  calked  to  drive  the  metal  into  the  threads, 
which  is  good  practice.  Stay-bolts  that  are  not  screwed  into 
the  sheets  should  be  passed  through  a  ferrule  or  distance-piece 
(Fig.  59)  to  prevent  the  sheet  from  being  bent  inward,  when  stay 
end  is  riveted  over  or  the  nuts  are  set  up.  If  the  ferrules  are 
omitted,  some  stays  may  carry  a  greater  load  than  adjacent  ones. 
The  great  objection  is  the  difficulty  of  getting  all  the  ferrules  of 
even  length,  while  many  claim  as  an  advantage  that  the  ferrules 
protect  the  stay  from  corrosion. 


FIG.  60. — Large   Stay  End  with 
Nut  and  Washer. 


FIG.  61 . — Larjre  Stay 
End  with  Double 
Nuts. 


These  small  stays  often  are  drilled  with  a  hole  about  J-  inch  in 
diameter  along  the  axial  line  to  act  as  a  tell-tale  (Fig.  56).  Should 
corrosion  eat  through  the  stay,  steam  will  blow  out  of  this  hole. 
It  is  common  practice  in  locomotive  work  to  drill  a  tell-tale  in 
every  second  stay  of  the  water-legs  of  .fire-box.  These  tell-tale 
holes  reduce  the  ability  of  the  stay  to  withstand  repeated  bending 
due  to  the  expansion  of  the  sheets.  See  paper  by  F.  J.  Cole,  Trans. 
Am.  Soc.  M.  E.,  June  1898. 


BOILER   DETAILS 


197 


All  large  stays  passing  through  the  sheets  should  be  fastened 
with  a  nut,  and  when  necessary  with  a  washer.  For  very  large 
stays,  or  for  stays  sustaining  heavy  pressures,  an  additional  nut  or 
lock-nut  on  the  inside  should  be  used  (Fig.  61).  When  double 
nuts  are  used,  the  stay  may  or  may  not  be  screwed  into  the 
plate,  but  a  much 
better  and  tighter  joint 
is  made  by  utilizing  the 
thread.  The  nuts  in  all 
cases  should  have  a 
shallow  groove  turned 
on  the  side  next  to  the 
plate  in  order  to  hold 
a  packing  (Fig.  62), 


FIG.  62. — Nut  for  Stays,  showing 
Packing  Groove. 


usually  made  of  as- 
bestos or  cotton  waste 
and  red  lead,  or  of 

cement.  When  screwed  into  the  plate,  one  end  of  large  stays  usually 
is  made  larger  than  the  other  by  about  J  inch,  so  as  to  allow  the 
stay  to  be  withdrawn.  The  larger  end  should  be  carefully  selected, 
so  that  the  stay  can  be  withdrawn  when  the  boiler  is  finally  located. 

Where  this  is  not  done,  these 
large  stays  often  have  to  be 
cut  and  removed  through  the 
manhole  in  pieces.  Such 
stays  when  cut  can  be  re- 
united by  upsetting  the  ends 
and  fastening  with  a  heavy 
coupling  or  turn-buckle,  but 
such  a  method  cannot  be 
recommended  except  for 
emergencies. 

Large  stays  can  be  fast- 
ened by  pins,  bolts  or  keys  to 
angles  or  tees  riveted  to  the 

FIG.  63. — Stay  End  with  Bolt  in         flat     sheets.       This     method 
Double  Shear.  placeg    the   rivetg  of  the  end 

attachments  in  tension,  which  is  objectionable,  but  allowable 
when  ample  rivet  section  is  provided.  Such  rivets  should  not  carry 


198 


STEAM-BOILERS 


over  6000  pounds  per  square  inch  of  sectional  area  The  bolts, 
etc.,  should  always  be  arranged  for  double  shear,  either  by  having 
double  eyes  on  the  stay  end  to  straddle  the  leg  of  the  tee  (Fig. 
63),  or  better  by  using  two  angles  with  the  stay  inserted  between 
them  (Fig.  64).  Sometimes  a  tee  end  is  forged  on  the  stay  end,  so 
as  to  carry  a  number  of  bolts  in  order  to  furnish  sufficient  bearing 
surface  to  make  them  equal  in  strength  to  the  body  of  the  stay. 

When  pins  are  used,  cotters  should  be  passed  through  the  ends 
(Figs.  63  and  64)  so  as  to  prevent  their  falling  out.  If  bolts  are  used, 
then  double  or  lock  nuts  are  to  be  preferred  to  single  nuts,  and  the 
bolt  so  placed  as  not  to  fall  out  by  gravity  should  the  nuts  be  acci- 


FIG. 


64.—  Stay  End  with  Bolt  in 
Double  Shear. 


FIG.  65.— A  Method  of  Fail- 
ure of  Fig.  64. 


dentally  removed.  If  n  ither  cotters  nor  nuts  be  used,  the  angles 
often  spread  apart,  and  the  pin  bends  under  the  increased  leverage, 
allowing  the  stay  to  become  slack  (Fig.  65). 

When  the  area  to  be  supported  is  small,  sufficient  strength 
is  often  secured  by  riveting  on  the  plate  a  tee  or  double  angles 
back  to  back.  The  angles  are  to  be  preferred,  and  are  best  ar- 
ranged radially  if  possible.  The  rivets  should  be  spaced  as  if  stay- 
bolts.  These  ribs  should,  however,  be  limited  to  small  areas  that 
cannot  be  otherwise  stayed,  or  to  boilers  designed  for  very  low 
pressures. 

Gusset-plates  are  often  used,  with  the  advantage  that  they  act 
over  large  areas  and  give  great  stiffness.  Gussets  should  always  be 
joined  by  double  angles  with  the  rivets  in  double  shear  (Fig.  66). 
Double  gussets  and  single  tees  are  not  to  be  relied  upon,  since  it  is 
practically  impossible  to  make  the  two  gussets  exactly  alike  in  shape 
and  material,  so  as  to  evenly  divide  the  load  to  be  supported.  The 
gussets  should  be  cut  away  so  as  not  to  come  too  close  to  the  corner 


BOILER  DETAILS 


199 


between  the  head  and  the  shell. 


FIG.  66.— Gusset  Plate  Stay. 


In  general  the  gusset  should  not 
be  nearer  than  four  inches, 
and  the  greater  the  distance 
the  better,  in  order  that  the 
head  may  have  sufficient 
"play"  to  prevent  grooving. 

Other  forms  of  stay  ends 
are  shown  in  Figs.  67,  68,  69 
and  70. 

Crown-sheets  of  fire-boxes 
are  stayed  either  directly  to 
the  shell  or  by  stay-bolts  to  a 
girder.  In  the  former  plan 
each  stay  is  made  as  nearly 
perpendicular  to  the  crown- 
sheet  as  possible.  In  con- 
sequence the  stays  often  meet 
the  shell  at  very  acute  angles, 
which  is  objectionable.  In 
order  to  avoid  this,  the  main 
boiler-shell  over  the  fire-box 
can  be  made  flat,  and  be  car- 
ried parallel  to  the  crown- 


sheet,  as  in  the  "Belpaire"  fire-box.  This  makes  a  large  throat- 
sheet  (the  sheet  joining  the 
fire-box  end  to  the  cylindrical 
part)  which  is  objected  to  by 
many  engineers  as  being  the 
weakest  sheet  in  the  shell. 

Direct  staying  of  the  crown 
makes  the  best  arrangement 
for  strength,  but  fills  up  the 
boiler  with  stays  and  thus 
renders  inspection,  cleaning 
and  scaling  difficult. 

The  girders  (Figs.  71  and 
72)  reach  across  the  crown-  FlG.  6?.— Stay  End  Fitted  to  Stirrup 


sheet  by  resting    on   the   end 


to  Distribute  the  Support. 


plates  of  the   fire-box,   forming   a  sort  of   bridge.      From  these 


200 


STEAM-BOILERS 


girders    stay-bolts   support    the    crown-sheet.        The    bottom    of 
these  girders  should  be  sufficiently  high  above  the  crown-sheet  (say 


FIG.  68. — Stay  End  Split  to  Form  Stirrup  to  Distribute  the  Support. 
a  b 


c 


FIG.  69. — Diagonal  Stay  with  rivets  through  palm  in  tandem  at  a,  and  in 
parallel  at  b.     The  form  at  b  considered  the  stronger. 

not  less  than  1|  inches,  depending  on  the  design)  to  enable  all 
scale  and  sediment  to  be  readily  removed.  The  stay-bolts  should 
have  ferrules. 


BOILER   DETAILS 


201 


Great  care  must  be  taken  to  rest  the  girder  ends  firmly  on  the 
end  plating  and  to  see  that  the  pressure  is  not  sufficient  to  crush 


FIG.  70. — Huston  Form  of  Stay  without  Weld. 


those  plates.  Girders  may  be  strengthened  by  having  stays 
fastened  to  the  shell.  In  Fig.  72  three  forms  of  such  stays  are 
shown. 

The  girders  can  be  made  of  forgings  of  steel  or  iron,  or  of  cast 
steel,  having  holes  for  the  stays  (Fig.  71);  or  of  two  pieces,  side  by 
side,  with  the  stays  between  (Fig.  72).  The  stay  ends  are  then 
supported  by  a  distance-washer,  and  the  two  half -girders  riveted  or 
bolted  together  through  spacing-pieces  or  ferrules. 

Stays  are  a  necessary  evil  in  all  boilers;  and,  as  they  are  apt  to 
give  trouble,  the  greatest  care  should  be  exercised  in  their  design 


FIG.  71. — Girder  Stay  for  Supporting  Crown-sheet. 

and  spacing.  They  should  be  arranged  so  as  not  to  obstruct  the 
operation  of  cleaning  and  scaling.  In  the  steam-space  they  should 
be  arranged  so  that  a  man  can  pass  between  them  when  they  are 
through  stays  from  head  to  head;  that  is,  be  about  14  inches 
centre  to  centre,  and  be  placed  in  horizontal  and  vertical  rows. 


202 


STEAM-BOILERS 


Small  stays,  in  narrow  spaces  like  water-legs,  must  be  arranged  to 
permit  a  cleaning-tool  to  be  inserted.  These  water-legs  should  be 
made  as  wide  as  convenient  to  suit  the  design.  The  inner  sheet, 
exposed  to  the  direct  heat  of  the  fire;  will  expand  more  than  the 


FIG.  72. — Girder  Stay  for  Supporting   Crown-sheet,  showing   three  forms  of 
strengthening  stays  to  shell. 

outer  shell,  and  is  liable, to  cause  rupture  of  stay-bolts  due  to  a 
repeated  bending  action.  As  the  amount  of  bending  is  constant, 
the  actual  bending  of  short  stays  will  be  greater  than  that  of  long 
ones,  and  the  former  will  therefore  fail  much  the  sooner.  When  the 
sheet  becomes  overheated  it  will  bulge  under  the  pressure,  and  this 
bulging  tends  to  open  the  hole  through  which  the  stay  passes  and 
permit  the  stay  end  to  be  drawn  through  the  sheet  under  a  pressure 
much  below  its  proper  holding  value.  The  nuts  are  made  one 
diameter  of  stay  in  length,  and  the  locking-nuts  about  f  as  long. 
The  screw-threads  should  be  a  fine  standard  V-shaped  gauge  with 
rounded  corners.  As  stays  are  apt  to  corrode  rapidly  and  are 
difficult  to  inspect,  they  should  be  proportioned  amply  heavy. 

The  load  that  is  carried  by  a  stay  depends  on  the  area  sup- 
ported and  the  pressure.  It  is  difficult  to  estimate  the  amount  of 
stiffness  due  to  the  flanged  edges  of  sheets,  but  it  is  safe  to  say  that 
they  will  be  self-supporting  for  a  distance  of  at  least  3  inches,  and  in 
heavy  sheets  for  considerably  more.  Furthermore,  the  tubes  will 
sustain  the  pressure  on  the  sheets  for  at  least  2  inches  beyond 


BOILER  DETAILS  203 

their  outer  surface,  and  more  than  that  when  the  sheets  are  thick. 
The  net  area,  then,  between  the  limits  defined  will  be  the  area  that 
must  be  sustained  by  the  stays. 

For  experiments  on  the  holding  power  of  stays,  reference  is  made 
to  "  Experiments  in  Boiler  Bracing/'  by  F.  J.  Cole,  Trans.  Am. 
Soc.  M.  E.,  Vol.  XVIII,  1897. 

Rules  for  Stays. 

1.   U.  S.  Hoard  of  Supervising   Inspectors  of  Steam-vessels. 

The  maximum  stress  in  pounds  allowable  per  square  inch  of  cross- 
sectional  area  for  stays  used  in  the  construction  of  marine  boilers,  when 
same  are  accurately  fitted  and  properly  secured,  shall  be  ascertained  by  the 
following  formula  : 


where  P=  working  pressure  in  pounds  ; 

A=  least  cross-sectional  area  of  stay  in  inches  ; 

a  =  area  of  surface  supported  by  one  stay,  in  inches  ; 

C=  a  constant,  6,000,  7,000,  8,000,  9,000,  as  the  case  may  be  ; 

(7=9,000  for  tested  steel  stays  exceeding  2i  inches  in  diameter  ; 

(7=8,000  for  tested  steel  stays  1J  inches  and  not  exceeding  2$  inches 
in  diameter,  when  such  stays  are  not  forged  or  welded.  The 
ends,  however,  may  be  upset  to  a  sufficient  diameter  to  allow 
for  the  depth  of  the  thread.  The  diameter  shall  be  taken  at 
the  bottom  of  the  thread,  provided  it  is  the  least  diameter  of 
the  stay.  All  such  stays  after  being  upset  shall  be  thoroughly 
annealed. 

C=8,000  for  a  tested  Huston  or  similar  type  of  brace,  the  cross- 
sectional  area  of  which  exceeds  5  square  inches  ; 

0=7,000  for  such  tested  braces  when  the  cross-sectional  a-rea  is  not 
less  than  1.227  and  not  more  than  5  square  inches,  provided 
such  braces  are  prepared  at  one  heat  from  a  solid  piece  of 
plate  without  welds  ; 

(7=6,000  for  all  stays  not  otherwise  provided  for. 

The  diameter  of  a  screw  stay  shall  be  taken  at  the  bottom  of  the  thread, 
provided  it  is  the  least  diameter  of  the  stay. 

For  all  stays  the  least  sectional  area  shall  be  taken  in  calculating  the 
stress  allowable. 

All  screw  stay-bolts  shall  be  drilled  at  the  ends  with  a  one-eighth  inch 
hole  to  at  least  a  depth  of  one-half  inch  beyond  the  inside  surface  of  the 
sheet.  Stays  through  laps  or  butt  straps  may  be  drilled  with  larger  hole 
to  a  depth  so  that  the  inner  end  of  said  larger  hole  shall  not  be  nearer  than 
the  thickness  of  the  boiler  plates  from  the  inner  surface  of  the  boiler. 

Such  screw  stay-bolts,  with  or  without  sockets,  may  be  used  in  the  con- 
struction of  marine  boilers  where  fresh  water  is  used  for  generating  steam: 
Ptwided,  however,  That  screw  stay-bolts  of  a  greater  length  than  24  inches 


204  STEAM-BOILERS 

will  not  be  allowed  in  any  instance,  unless  the  ends  of  said  bolts  are  fitted 
with  nuts.  Water  used  from  a  surface  condenser  shall  be  deemed  fresh  water. 

Holes  for  screwed  stays  must  be  tapped  fair  and  true,  and  full  thread. 

The  ends  of  stays  which  are  upset  to  include  the  depth  of  thread  shall 
be  thoroughly  annealed  after  being  upset. 

The  sectional  area  of  pins  to  resist  double  shear  and  bending,  accurately 
fitted  and  secured  in  crow-feet,  sling,  and  similar  stays,  shall  be  at  least 
equal  to  required  sectional  area  of  the  brace.  Breadi'h  across  each  side 
and  depth  to  crown  of  eye  shall  be  not  less  than  .35  to  .55  of  diameter  of 
pin.  In  order  to  compensate  for  inaccurate  distribution  the  forks  should 
be  proportioned  to  support  two-thirds  of  the  load,  thickness  of  forks  to  be 
net  less  than  .66  to  .75  of  the  diameter  of  pins. 

The  combined  sectional  area  of  rivets  used  in  securing  tee  irons  and 
crow-feet  to  shell,  said  rivets  being  in  tension,  shall  be  not  less  than  the 
required  sectional  area  of  brace.  To  insure  a  well-proportioned  rivet  point, 
the  total  length  of  shank  shall  closely  approximate  the  grip  plus  1.5  times 
the  diameter  of  the  shank.  All  rivet-holes  shall  be  drilled.  Distance  from 
center  of  rivet-hole  to  edge  of  tee  irons,  crow-feet,  and  similar  fastenings 
shall  be  so  proportioned  that  the  net  sectional  areas  through  sides  at  rivet- 
holes  shall  equal  the  required  rivet  section.  Rivet-holes  shall  be  slightly 
countersunk  in  order  to  form  a  fillet  at  point  and  head. 

2.  Lloyd's  Rule. 

The  strength  of  stays  supporting  flat  surfaces  is  to  be  calculated  from 
the  smallest  part  of  the  stay  or  fastening;  the  strain  upon  them  is  not  to 
exceed  the  following  limits: 

Iron  Stays.  For  stays  not  exceeding  H  inches  effective  diameter,  and 
for  all  stays  which  are  welded,  6000  pounds  per  square  inch.  For  un welded 
stays  above  1  £  inches  effective  diameter,  7500  pounds  per  square  inch. 

Steel  Stays.  For  screw  stays  not  exceeding  1£  inches  effective  diameter, 
8000  pounds  per  square  inch;  for  screw  stays  above  H  inches  effective 
diameter,  9000  pounds  per  square  inch.  For  other  stays  not  exceeding  l£ 
inches,  9000  pounds  per  square  inch,  and  for  stays  exceeding  1|  inches, 
10,000  pounds.  No  steel  stays  are  to  be  welded. 

Stay-tubes.     The  stress  is  not  to  exceed  7500  pounds  per  square  inch. 

Note. — The  size  of  angles  riveted  to  flat  surfaces  to  act  as  stays 
can  be  determined  by  rule  for  "Flat  Surfaces."  The  stress  on  any 
stay  is  determined  by  the  area  supported  and  the  pressure.  No 
allowance  is  made  for  any  additional  strength  in  the  flat  surface. 
If  the  stays  are  diagonal  to  the  flat  surface  supported,  the  stress  in 
the  stay  is  found  by  dividing  the  pressure  on  total  surface  supported 
by  the  cosine  of  the  angle.  The  area  of  small  gussets  should  be 
made  heavier  than  that  required  by  actual  calculation,  lest  all  the 
stress  should  come  on  one  edge. 


BOILER   DETAILS  205 

Girders.  The  rule  of  the  U.  S.  Inspectors  is  the  same  as 
that  of  the  Board  of  Trade,  except  c=825  when  two  or  three 
supporting  bolts  are  fitted,  and  c=935  when  four  bolts  are  fitted. 
The  bolts  are  proportioned  by  the  rules  for  stays.  It  is  usual  to 
make  the  thickness  J  the  depth  in  short  girders  and  ^  in  long 
ones. 

The  rule  of  the  Board  of  Trade  (British)  is  as  follows: 

When  the  tops  of  combustion-boxes  or  other  parts  of  a  boiler  are 
supported  by  solid  girders  of  rectangular  section,  the  following  formula 
should  be  used  for  finding  the  working  pressure  to  be  allowed  for  the 
girders,  assuming  that  they  are  not  subjected  to  a  greater  temperature 
than  the  ordinary  heat  of  steam,  and  in  the  case  of  combustion-cham- 
bers that  the  ends  are  properly  bedded  to  the  edges  of  the  tube-plate, 
and  the  back  plate  of  the  combustion-box : 

Cxd2xT 
\V  orki  ng  pressure  =  p  =  -,  TT/r — j 


(W-P)DxL 

where  W  denotes  width  of  combustion-box  in  inches; 
P  "  pitch  of  supporting  bolts  in  inches; 
D  "  distance  between  the  girders  from  centre  to  centre  in 

inches ; 

L        "        length  of  girder  in  feet; 
d         "        depth  of  girder  in  inches; 
T  thickness  of  girder  in  inches; 

N       "        number  of  supporting  bolts; 

C        "        ^-1002  when  number  of  bolts  is  odd  ; 

(Ar  +  l)XlOOO     , 
C  — when  number  of  bolts  is  even. 

The  working  pressure  for  the  supporting  bolts  and  for  the  plate 
between  them  should  be  determined  by  the  rules  for  ordinary  stays 
and  plates. 

Combustion-chamber  is  the  name  given  to  that  part  behind 
the  bridge-wall  in  which  the  gases  are  expected  to  mix  and  burn. 
The  term  is,  however,  applied  to  different  parts  according  to  the 
design.  In  general  the  combustion-chamber  should  be  as  large  as 
possible,  and  many  boilers  are  now  being  arranged  so  as  to  keep  the 
furnace  proper  away  from  the  boiler,  that  the  combustion  may  be 
completed  before  the  products  are  cooled  by  the  water  surfaces. 


206  STEAM-BOILERS 

In  the  ordinary  vertical  boiler  there  is  no  combustion-chamber 
other  than  the  furnace.  Messrs.  Dean  and  Main  have  designed  a 
vertical  boiler  of  large  size  (See  Engineering  News,  June  23,  1898)  in 
which  the  height  from  grate  to  tube-sheet  is  8  feet. 

Good  results  have  been  obtained  by  standing  the  vertical  boiler 
of  ordinary  design  on  top  of  a  brick  furnace,  in  order  to  procure 
additional  height  in  the  combustion-chamber. 

In  externally  fired  cylindrical  boilers  the  combustion-chamber  is 
the  space  behind  the  bridge- wall,  arid  as  generally  set  the  space  is 
large  enough.  Where  such  boilers  have  return  tubes,  the  distance 
between  the  back  head  and  the  rear  wall  of  setting  is  about  18 
inches  for  small  boilers  and  24  inches  to  30  inches  for  large  ones. 

In  internally  fired  boilers  of  the  Cornish  and  Lancashire  types 
the  combustion-chamber  is  the  space  in  the  flues  behind  the  bridge, 
and  is  as  large  as  can  be  obtained.  In  vertical  and  locomotive  boilers 
the  furnace  forms  the  combustion-chamber.  Sometimes  a  fire- 
brick arch  supported  on  water-circulating  tubes  is  placed  over  part 
of  the  fire,  and  its  action  is  similar  to  that  of  a  bridge  to  mix  the 
gases.  The  space  above  might  then  be  called  a  combustion- 
chamber. 

In  Scotch  and  in  Flue  and  Return-Tube,  or  sometimes 
called  "Marine"  boilers,  the  combustion-chamber  is  a  box  con- 
structed inside  the  boiler  and  acts  as  a  connection  between  the 
tubes  and  flues.  It  is,  therefore,  called  a  "back  connection."  In 
boilers  of  the  " Marine"  type  there  is  often  a  " front  connection" 
to  connect  the  tubes  to  the  uptake  or  the  liner  of  the  steam-drum, 
or  steam-chimney. 

The  capacity  of  the  combustion-chamber  in  Scotch  and  similar 
boilers  should  be  not  less  than  that  of  the  furnace-flues  entering 
into  it,  when  the  boiler  is  single-ended,  but  may  be  slightly 
less  when  double-ended.  The  back  and  tube  plates  are  flanged 
in,  and  the  sides  and  top  are  riveted  on  the  outside.  This  ar- 
rangement always  leaves  the  calking  edge  exposed.  The  water- 
space  between  the  sides  and  bottom  of  the  chamber  and  the  shell 
should  not  be  less  than  3  inches  in  the  clear,  but  4^  or  5  inches  is 
much  better.  In  general,  the  wider  the  space  the  better  the  circu- 
lation. Sometimes  the  bottom  of  the  chamber  has  to  be  rounded 
up  between  the  flues  so  that  a  manhole  may  be  provided  in  the  back 
head.  The  chamber  can  then  be  stiffened  by  angles  running  across 


BOILER  DETAILS  207 

the  boiler,  as  ordinary  stays  cannot  be  used.  The  back  plate  of  the 
chamber  is  made  parallel  to  the  back  head  in  many  boilers,  but  it 
is  better  to  make  it  slant  slightly  that  the  water-space  may  be 
wider  at  the  top  to  facilitate  the  separation  of  steam.  The  space 
at  the  bottom  is  made  about  4  to  6  inches  and  widens  to  8 
or  9  inches  at  the  top.  The  bottom  plate  should  be  at  least  TV 
inch  thicker  than  the  sides  in  order  to  provide  for  corrosion.  The 
top  plate  should  be  the  same  as  the  bottom.  The  tube-plate  is 
usually  about  T\-  or  f-inch,  but  varies  from  J-  to  J-inch.  The  back 
plate  is  generally  J-  or  T\-inch,  but  the  thickness  is  dependent 
on  the  distance  between  stay  centres,  and  the  stays  should  be  so 
arranged  as  to  give  a  thickness  as  above.  If  very  high  pressures 
are  used  the  thicknesses  are  slightly  increased  over  the  figures  just 
given. 

In  Scotch  boilers  with  natural  draft,  one  chamber  may  be  used 
common  to  all  furnaces,  but  with  forced  drafts  it  is  better  to  have 
separate  combustion-chambers.  Separate  chambers  add  weight 
and  are  more  expensive,  but  facilitate  the  generation  of  steam  and 
interfere  least  with  the  draft. 

In  single-ended  boilers  many  engineers  place  a  manhole  into 
the  chamber  through  the  rear  plate,  but  this  is  not  necessary  if  the 
flues  are  large  enough  to  admit  a  man  over  the  bridge-wall.  When 
so  made,  the  rear  head  and  back  plate  of  chamber  are  flanged,  and 
provision  has  to  be  made  to  drive  the  rivets.  These  back  entrances 
are  of  little  value,  and  unless  absolutely  necessary  had  better  be 
omitted,  as  the  joint  often  causes  trouble  if  not  extremely  well 
made. 

Riveting.  The  riveted  joints  are  usually  the  weakest  part  in  a 
boiler,  and  as  they  often  leak  and  give  trouble,  the  greatest  care 
should  be  bestowed  upon  them. 

The  average  riveter  requires  a  space  of  24  inches  to  drive  a  rivet 
by  hand,  but  some  few  experts  can  close  a  rivet  in  16  inches. 
Allowance  for  riveting  often  determines  the  spaces  that  must  be 
made  in  the  design. 

In.  order  to  be  tight,  rivets  should  be  driven  from  the  water, 
steam  or  pressure  side. 

The  joints  may  be  single-,  double-,  or  treble-riveted,  etc.,  accord- 
ing to  the  number  of  rows  of  rivets  driven  in  each  plate.  In  order 
to  make  the  joint,  the  edges  of  the  plates  may  be  lapped,  or  lapped 


208 


STEAM-BOILERS 


and  strapped,  or  butt-jointed  with  single  or  double  straps,  welt- 
strips  or  cover-plates  (Figs.  73,  74,  75,  76  and  77). 

When  in  multiple  rows  the  rivets  may  be  arranged  as  " chain" 
riveting,  that  is,  one  directly  behind  the  other,  or  as  "  zigzag,"  that 
is,  staggered.  The  latter  is  much  the  better  for  boiler  work.  The 


FIG.  73. — Single  Riveted  Lapped  Joint. 

11  pitch"  is  the  distance  between  centres  of  rivets  in  one  row,  and 
the  ''spacing"  is  the  distance  between  centre  lines  of  rows. 

The  "tail"  of  the  rivet  is  formed  on  the  rivet  when  purchased, 
and  the  "head"  is  made  on  the  shank  end  when  in  place.  The 
shape  of  the  head  is  either  conical  or  semi-spherical,  the  latter 
called  a  "cup"  head.  The  conical  head  (Fig.  79)  is  most  common 
in  hand-work.  The  height  of  the  cone  should  be  f  or  J  the  diameter 
of  shank,  and  the  greatest  diameter  of  the  cone  about  If  times  the 
diameter  of  the  shank.  If  the  cone  head  be  not  made  concentric 
with  the  shank,  the  head  will  not  properly  cover  the  hole  in  the  plate 


BOILER  DETAILS 


209 


and  will  make  a  weak  rivet.     As  it  may  be  difficult  to  note  the 
amount  of  eccentricity,  the  cone  makes  a  poor  form  for  the  head. 


FIG.  74.— Double    Riveted  Lapped  Joint. 

It  is  also  a  poor  shape,  due  to  the  thinness  of  the  edges,  where  it  is 
liable  to  be  rapidly  corroded.  The  spherical  or  cup  head  (Fig.  77) 
is  the  better  form,  and  is  mads  by  a  cup-shaped  die  placed  over  the 


210 


STEAM-BOILERS 


head  while  being  formed.     The  height  of  the  cup  should  be  f  or  J, 
the  diameter  of  shank,  and  the  greatest  diameter  If  times  the  diam- 


FIG.  75. — Single  Riveted  Lapped  and  Strapped  Joint. 

eter  of  shank.     The  bottom  edge  should  not  be  at  right  angles  to  the 
plate,  that  is,  the  head  is  somewhat  less  than  a  semi-sphere.     This 


BOILER  DETAILS 


211 


permits  the  edge  to  be  calked  more  easily,  and  allows  for  any  surplus 
metal  to  flow  out  from  under  the  die. 

The  tails  are  either  cup-  or  button-shaped,  the  latter  sometimes 
called       pan-shaped     __ 
(Fig.  76). 

The  allowance  of 
length  of  shank  for 
forming  the  head  is 
about  1|  times  the 
diameter  for  both 
conical  and  spherical 
heads  when  hand- 
driven;  but  about  -j1^- 
to  J-inch  more  when 
machine-driven.  In 
addition  to  the  above, 
there  should  be  an 
allowance  of  T1g-inch 
for  each  plate  when 
more  than  two  are 
connected. 

Counter-sunk  riv- 
ets should  be  avoided 
as  much  as  possible. 
The  plate  is  weakened 
by  having  so  much 
metal  cut  away,  and 
the  head  is  more  apt 
to  pull  through  the 
plate.  Counter-sunk 
heads  are  liable  to 
leak  and  are  difficult 
to  calk.  Such  rivets 
are  only  permissible 
when  they  are  placed 
under  flanges  or 
fittings  or  in  laps  not  subject  to  tension,  and  in  direct  line  with 
the  play  of  the  flames,  as,  for  instance,  in  the  flange  of  furnace  flues 
(Fig.  78). 


FlG' 


**** 


212 


STEAM-BOILERS 


FIG.  77. — Treble  Riveted  Butt  Joint,  with  straps  of  unequal  widths. 


BOILER  DETAILS  213 

It  must  be  remembered  that  the  object  of  boiler-riveting  is  not 
only  to  join  the  plates,  but  to  help  form  a  water-tight  joint,  and  the 
rivets  have  to  be  pitched  with  this  object  also  in  view.  The  pitch 
of  the  outside  row  of  rivets  next  to  the  edge  of  any  plate  should 
never  exceed  seven  thicknesses  of  plate,  in  order  to  keep  the  plates 
from  springing  apart  between  the  rivets.*  To  complete  the  tight- 
ness of  the  joint,  the  edges  of  the  plates  are  calked  both  inside  and 


FicJ.  78. — Joint  between  Tube  Sheet  and  Furnace  Flue,  showing  countersunk 
rivet  where  exposed  to  the  fire. 

outside.  The  calking  tool  always  should  be  round-pointed  and  never 
square  or  sharp,  as  the  latter  is  liable  to  injure  the  plates  by  forming 
a  slight  groove,  which  will  increase  rapidly  by  corrosion  and  by  the 
working  of  the  plates  under  expansion  and  contraction.  That  the 
calking  may  be  more  properly  done,  the  edges  of  the  plates  should  be 
planed  to  a  slight  bevel. 

Rivets  always  should  be  driven  hot,  as  they  are  less  liable  to  be 
injured  than  when  cold-driven. 

Rivets  may  be  driven  by  hand,  but  the  work  is  much  better 
performed  by  power,  since  the  shank  is  made  to  more  completely 
fill  the  hole  before  the  head  is  formed,  and  there  is  less  chance  of  the 
rivet  getting  cold  due  to  the  quickness  of  the  operation.  Against 
machine-riveting  it  is  sometimes  urged  that  the  shank  may  bulge 

*  If  the  joint  is  at  least  double-riveted,  and  the  plate  f-inch  or  thicker, 
the  maximum  pitch  may  be  seven  and  a  half  thicknesses. 


214  STEAM-BOILERS 

under  the  heavy  pressure  and  force  the  plates  apart.  While  this  ob- 
jection does  not  seem  to  be  sustained  by  practice,  many  of  the  rivet- 
ing-machines have  a  device  for  holding  the  plates  'together  during 
the  operation.  Machines  will  satisfactorily  close  rivets  that  are  so 
large  as  to  be  dangerous  to  work  by  hand  for  fear  of  creating  hidden 
defects. 

Power  riveting-machines  are  operated  by  either  gearing,  water, 
steam  or  compressed  air.  In  general,  the  hydraulic  machines  are 
preferred,  since  the  work  is  done  more  gradually  and  with  less  of  a 
shock  or  blow.  The  slower  and  steadier  pressure  of  the  water  causes 
the  shank  to  swell  throughout  its  length,  thus  filling  the  hole,  while 
under  a  violent  blow  the  head  may  be  formed  first,  thus  leaving  the 
shank  loose.  Dr.  Coleman  Sellers  introduced  an  improvement  in 
the  steam-riveter,  which  is  also  applicable  to  compressed  air,  by 
adopting  a  small  supply-pipe.  This  prevents  the  piston  from  ad- 
vancing rapidly  and  causes  it  to  act  in  imitation  of  the  hydraulic 
ram.  The  hydraulic  pressure  usually  maintained  is  1500  to  1600 
pounds  per  square  inch,  or  about  100  atmospheres. 

The  pressure  put  upon  a  rivet  should  be  in  proportion  to  the  size 
of  rivet,  and  machines  are  made  of  varying  total  capacities  from  a 
few  tons  to  150  tons,  which  is  about  the  heaviest  machine  in  use  at 
the  present  time.  If  too  great  a  pressure  be  placed  upon  the  rivets, 
the  plates  will  stretch  along  the  seam.  On  the  other  hand,  in  order 
to  insure  tight  work,  boiler-rivets  require  a  heavier  pressure  than 
ordinary  rivets  as  used  in  structural  work.  For  hot  rivets,  a  pres- 
sure of  50  tons  or  100,000  pounds  per  square  inch  of  area  has  been 
found  ample  when  the  rivets  are  short,  and  a  slightly  greater  pres- 
sure with  a  slower  movement  of  the  ram  when  the  rivets  are  long. 
For  f-inch  rivets  driven  cold,  a  pressure  of  15  tons  or  30,000  pounds 
has  been  found  sufficient,  while  at  20  tons  the  metal  in  the  plates 
has  stretched.  A  pressure  of  40  tons  on  an  inch  rivet  driven 
hot  has  given  good  results,  although  many  use  a  lower  pressure.  A 
machine  capable  of  exerting  60  tons  on  the  rivet  is  generally  con- 
sidered amply  heavy  for  the  largest-sized  rivet  likely  to  be  used  in 
ordinary  boiler  construction. 

The  strength  of  rivets  to  resist  shearing  is  sometimes  erroneously 
taken  as  equal  to  the  tensile  strength  of  the  metal.  The  shearing 
strength  of  iron  rivets  may  be  taken  as  80  per  cent  of  the  tensile 
strength,  and  of  steel  rivets  as  75  per  cent.  Rivets  in  double  shear 


BOILER   DETAILS 


215 


are  from  1.75  to  1.80  times  as  strong  as  those  in  single  shear.  Resist- 
ance to  failure  by  shearing  is  increased  by  the  friction  between  the 
plates.  This  friction  may  amount  to  three  or  even  seven  tons  per 
rivet.  No  allowance  is  made  for  this  friction  in  determining  the 


FIG.  79.— Good  and  Bad  Calking. 


FIG.  80.— Effect  of  Indirect  Pull  on  a  Lapped  Joint. 


FIG.  81. — Effect  of  Indirect  Pull  on  a  Single  Strapped  Joint 

strength  of  joint,  as  it  is  very  unreliable.  In  all  lap-joints  the 
tendency,  due  to  the  indirect  pull,  is  to  open  the  joint  and 
neutralize  the  friction.  Imperfect  calking  is  apt,  especially  with 
thin  plates,  to  open  the  seam  (Fig.  79).  The  effect  of  this  indirect 
pull  on  lapped  joints  is  shown  in  Figs.  80  and  81.  With  thick 
plates  the  tendency  to  distort  the  joint  will  be  greater.  In  double- 


216 


STEAM-BOILERS 


000000.0 
0000000 


ooooooooo 


strapped  butt-joints  the  force  acts  in  a  straight  line,  and  there  is 
no  tendency  for  the  joint  to  open.  All  longitudinal  seams  in 
important  boilers,  therefore,  should  be  double-strapped. 

The  continual  bending  action  in  lapped  joints  and  in  single- 
strapped  butt-joints  often  causes  cracks  to  form  beneath  the  lap,* 
as  shown  in  Fig.  82.  These  cracks  widen  by  corrosion,  and  being 

always  hidden  under  the 
lap,  are  very  dangerous. 
When  single  straps  are 
used,  they  always  should 
be  applied  on  the  outside 
of  the  shell.  If  placed  in- 
ternally, the  tendency  to 
open  at  the  butt  is  in- 
creased. 

Long  rivets  in  boiler 
work  should  be  avoided, 
as  the  heads  are  liable  to 
fly  off  after  the  rivets  have 
been  driven,  probably  due  to 
internal  stress  while  cooling. 
The  greatest  mass  of  metal 
is  where  the  head  joins  the  shank,  and  this  part  retains  the  heat 
longest.  Then  as  the  rivet  cools  and  contracts,  stresses  are  set  up  at 
this  point  which  may  at  any  time  cause  the  failure  of  the  rivet. 
These  stresses  are  increased  by  the  length  of  shank.  '  Rivets  never 
should  be  driven  through  more  than  three  full  thicknesses  of  plate, 
and  then  only  with  the  greatest  care. 

Boiler-rivets  should  be  tested  for  tightness  by  striking  the  head 
a  sharp  blow  with  a  hammer  while  the  thumb  is  placed  on  rivet 
and  forefinger  on  plate.  Any  slight  movement  can  then  be  detected 
after  a  little  experience. 

The  rivet-hole  is  made  TV  inch  larger  than  the  cold  rivet,  so 
that  it  may  be  inserted  when  hot. 

It  is  of  great  importance  that  the  holes  should  match  fair  and 
not  overlap  or  be  "partly  blind."  If  they  be  unfair,  the  rivets  will 
not  fill  the  holes  and  a  leak  is  apt  to  occur.  The  holes  should 


FIG.  82. — Cracks  in  Lapped  Joint  due 
to  Bending. 


*  Many   sample    cases   are    illustrated   in   Locomotive  (Hartford    Steam 
Boiler  Inspection  and  Insurance  Co.),  January,  1897. 


BOILER   DETAILS  217 

never  be  forced  to  match  by  using  a  drift-pin,  which  only  weakens 
the  plates  by  stretching  them  beyond  their  elastic  limit.  When  the 
holes  are  not  fair  it  is  best  to  ream  them  out  and  use  a  larger  rivet. 

The  holes  are  either  punched  or  drilled.  Wrought  iron  and  the 
mildest  grades  of  steel  are  not  seriously  affected  by  punching. 
Ordinary  boiler  steel,  especially  the  harder  grades,  is  injured  by 
punching,  and  the  effect  extends  a  variable  distance,  accord- 
ing to  the  thickness  of  plate  and  size  of  hole.  As  the  injury 
is  not  visible  and  can  only  be  made  apparent  by  etching  with  acid, 
a  test  not  practicable  in  boiler  construction,  even  the  mildest  steel 
should  not  be  punched  lest  an  undetected  flaw  be  created.  Steel 
plates  should  be  drilled  and  have  the  burr  formed  by  the  drill 
removed.  There  is  little  danger,  however,  in  punching  thin,  mild 
steel  plates  and  then  reaming,  so  as  to  remove  at  least  y^-inch  of 
metal  around  the  hole.  The  best  practice  is  to  drill  both  plates  to- 
gether after  they  have  been  rolled  to  shape,  and  thus  insure  per- 
fect fairness  of  holes.  Drilling  is  more  accurate  than  punching, 
but  is  slower,  while  punching  is  cheaper  and  practised  by  some 
boilermakers  on  that  account. 

From  tests  made  on  steel  plates,  it  appears  that  thin  plates  suffer 
least  from  punching,  but  when  thicker  than  f-inch,  the  loss  due  to 
punching  varies  from  6  per  cent  to  33  per  cent.  This  loss  may  be 
partially,  and  in  some  cases  totally,  removed  by  subsequent  anneal- 
ing. It  is  claimed  that  rivets  are  more  easily  sheared  in  drilled 
than  in  punched  holes,  but  this  is  probably  not  the  case  if  the 
sharp  corners  of  the  drilled  holes  be  slightly  rounded  with  a  file, 
as  they  should  be  in  all  important  work. 

The  end  of  the  punch  should  be  slightly  concave,  with  the  diam- 
eter of  the  cutting  edge  a  trifle  larger  than  the  shank,  so  as  to  make 
a  clean  cut.  The  hole  in 
the  die  is  somewhat  larger 
than  the  punch,  in  order  that 

no  resistance  may  be  offered 

c    .,  FIG.  83. — Rivets  in  Punched  Holes, 

to  the  action  ot   the  punch 

or  the  discharge  of  the  "wad."  The  diameters  are  usually  in  the 
ratio  of  1  to  1.1  or  1.2.  This  produces  a  conical-shaped  hole.  The 
plates  should  be  put  together  so  that  the  small  diameters  are  at 
the  centre.  The  swelling  of  the  shank  of  the  rivet  will  then  assist 
the  head  in  holding  the  plates.  If  placed  otherwise  the  swelling  of 
the  rivet  may  wedge  the  plates  apart  (Fig.  83). 


218  STEAM-BOILERS 

The  strength  of  a  riveted  joint  is  always  less  than  that  of  the 
plate,  on  account  of  the  plate  being  weakened  by  the  metal  cut  away 
by  the  holes.-  The  strength  of  the  joint  should  be  calculated  and  a 
proper  factor  of  safety  used  to  determine  the  allowed  safe  pres- 
sure. A  long  line  of  rivets  is  considered  stronger  than  a  few  as 
used  for  testing  purposes,  and  also  the  plate  between  the  holes 
is  considered  stronger  than  its  actual  tensile  strength.  These  ele- 
ments of  strength  are  not  considered  in  the  calculation,  as  they 
are  too  variable  and  difficult  to  credit  with  proper  values. 

A  riveted  seam  fails  in  one  of  the  following  ways : 

1.  By  the  shearing  of  the  rivets; 

2.  By  the  plate  breaking  between  the  holes; 

3.  By  the  plate  breaking  between  the  holes  and  edge; 

4.  By  the  plate  crushing  in  front  of  the  rivet;* 

5.  By  the  plate  shearing  in  front  of  the  rivet. 

In  general  a  line  of  fracture  includes  more  than  one  of  the  above 
five  conditions,  for  when  the  rupture  once  takes  place  it  often  does 
not  have  time  to  follow  the  line  of  least  resistance  and  new  stresses 
are  brought  to  bear,  so  that  it  frequently  becomes  difficult  from  an 
examination  of  the  rent  to  determine  just  where  the  break  first 
occurred. 

In  order  to  supply  ample  strength  to  resist  the  third,  fourth  and 
fifth  conditions,  practice  dictates  that  the  distance  from  hole  to  edge 
of  plate  should  be  at  least  equal  to  diameter  of  rivet. 

Plates  usually  fail  first  by  tearing  between  the  rivet-holes, 
caused  by  brittleness  of  plate,  injury  due  to  punching,  expansion  and 
contraction  stresses  and  loss  of  section  due  to  corrosion.  As  the 
rivet  is  protected  under  ordinary  conditions  from  corrosive  effects, 
it  is  well  to  design  new  boilers  so  that  there  shall  be  a  small  increase 
in  the  strength  of  plate  between  holes  over  the  shearing  strength 
of  rivets. 

The  strength  of  the  joint  is  calculated  for  every  possible  class  of 
failure.  The  lowest  strength  so  found  when  compared  with  the 
strength  of  solid  plate,  expressed  in  percentage,  is  called  the  effi- 
ciency of  the  joint. 

The  method  of  calculating  the  efficiency  of  riveted  joints,  when 


*  The  crushing  strength  can  be  taken  at  90,000  Ibs.  to  95,000  Ibs.  per 
square  inch  on  an  area  equal  to  the  diameter  of  rivet-hole  times  the  thick- 
ness of  plate. 


BOILER  DETAILS  219 

the  rivets  are  properly  spaced  back  from  the  edge  and  between  rows, 
is  as  follows: 

SINGLE-RIVETED  JOINT 

Steel  plate,  tensile  strength  per  square  inch  of  section,  60,000  Ibs.; 

Thickness  of  plate,  |  inch  =  0.375  ; 

Diameter  rivet-holes,  |f  in.  =  0.8125; 

Area  of  rivet-hole  =  0.5185  sq.  in.; 

Pitch  of  rivets,  If  in.  =  1.875; 

Shearing  resistance  of  steel  rivets  per  square  inch  =  45,000  Ibs. ; 

Then  1.875X0.375X60,000  =  42, 187  =  strength  of  solid  plate; 

(1.875-0.8125) X 0.375X60,000  =  23,906  lbs.=strength  of  net 

section  of  plate; 
0.5185 X45',000  =  23,332  lbs.  =  strength  of  one  rivet  in  single 

shear. 

The  rivet  strength  is  the  weakest;  therefore  23,332^42,187  = 
55.3  per  cent  efficiency  of  joint. 

DOUBLE-RIVETED  JOINT 

In  double-riveted  lap-joints  an  accession  of  strength  is  found 
over  the  single-riveted  joint  of  about  20  per  cent.  This  arises  from 
the  wider  lap  and  the  better  distribution  of  the  material.  The 
rivets  are  pitched  wider,  and  there  is  more  rivet  area  to  be 
sheared,  together  with  a  larger  percentage  of  net  section  of  plate 
to  be  broken. 

Steel  plate,  tensile  strength  per  square  inch  of  section,  60,000  Ibs. ; 
Thickness  of  plate,  f  inch  =  0.375; 
Diameter  of  rivet-holes,  |f  in.  =  0.8125; 
Area  rivet-hole  =  0.5 185  sq.  in.; 
Pitch  of  rivets  =  2. 5  in.; 

Shearing  resistance  of  steel  rivets  per  square  inch,  45,000  Ibs.; 
Then  2.5X0.375X60,000  =  56,250  lbs.  =  strength  of  solid  plate; 

(2.5- 0.8125)  X 0.375X60,000  =  37,969    Ibs.  =  strength   of    net 

section  of  plate ; 
0.5185X2X45,000  =  46,665  =  strength  of  two   rivets  in  single 

shear. 

Net  section  of  plate  is  the  weakest;  therefore  37,969-^-56,250  = 
67.5  per  cent  efficiency  of  joint. 


220  STEAM-BOILERS 


TRIPLE-RIVETED  JOINT 

In  a  triple  lap-riveted  joint  there  is  a  gain  in  strength  for  reasons 
similar  to  those  above. 

Steel  plate,  tensile  strength  per  square  inch  of  section,  60,000  Ibs. ; 
Thickness  of  plate,  f  in.  =  0.375; 
Diameter  of  rivet-holes,  if  inch  =0.8125; 
Area  one  rivet-hole  =  0.5185  sq.  in.; 
Pitch  of  rivets  =  3J  in.  =  3.5; 

Shearing  resistance  of  steel  rivets  per  square  inch,  45,000  Ibs.  ; 
Then  3.5X0.375X60,000  =  78,750  Ibs.  =  strength  of  solid  plate; 

(3.5-0.8125) X 0.375X60,000  =  60,469    lbs.  =  strength    of    net 

section  of  plate. 
0.5185X3X45,000  =  69,997  Ibs.  =  strength  of  three  rivets  in 

single  shear. 
Net  section  of  plate  is  the  weakest,  and  efficiency  is  76.7%. 

DOUBLE-RIVETED,  DOUBLE-STRAPPED  BUTT-JOIXT 

This  joint  is  calculated  the  same  as  a  double-riveted  joint,  except 
that  the  shearing  strength  of  the  rivets  is  increased  for  double  shear. 

TRIPLE-RIVETED  DOUBLE-STRAPPED  BUTT-JOINT 

When  inner  and  outer  straps  have  the  same  width. 
Steel  plate,  tensile  strength  per  square  inch  of  section,  60,000  Ibs. ; 
Thickness  of  plate,  |  inch  =  0.375; 
Diameter  of  rivet-holes  =  [f  inch  =  0.8125; 
Area  of  rivet-holes  =  0.5 185  sq.  in.; 
Pitch  of  rivets,  3^  inches  =  3.5; 

Resistance  of  steel  rivets  in  double  shear,  78,750  Ibs. ; 
Then  3. 5X0. 375X60,090  =  78,759  Ibs.  =  strength  of  solid  plate; 

(3.5- 0.8125)  X 0.375X60,000  =  60,469   Ibs.  =  strength    of    net 

section  of  plate; 
0.5185X3X78,750  =  122,495  Ibs.  =  strength  of  three  rivets  in 

double  shear. 

Net  section  of  plate  is  the  weakest,  and  efficiency  is  76.7%. 
..  This  is  not  a  well-proportioned  joint,  because  the  rivet  strength 
is  too  great.     The  rivets  should  have  been  spaced  farther  apart; 
although  there  is  no  advantage  in  treble  riveting  plates  as  thin  as 


BOILER   DETAILS  221 

f-inch.     The  selection  was  made  simply  to  show  the  method  em- 
ployed and  to  afford  comparison  with  the  next  case. 

When  the  inner  strap  is  wider  than  the  outer  strap,  and  the 
pitch  of  the  outside  row  of  rivets  is  twice  that  of  the  inside  rows. 
The  rivets  in  the  outside  row  now  are  in  single  shear.     This  arrange- 
ment increases  the  net  section  of  plate  *  and  reduces  the  area  of 
rivets  to  be  sheared,  thereby  increasing  the  efficiency  of  the  joint. 
Steel  plate,  tensile  strength  per  square  inch  of  section,  60,000  Ibs.; 
Thickness  of  plate,  f  inch  =  0.375; 
Diameter  of  rivet-holes,  -[f  inch  =  0.8125; 
Area  of  rivet-hole  =  0.5185  sq.  in.; 
Pitch  of  rivets  in  inner  rows,  3^  inches  =  3. 5; 
Pitch  of  rivets  in  outer  rows,  7  inches  ; 
Resistance  of  steel  rivets  in  single  shear,  45,000  Ibs.; 
Resistance  of  steel  rivets  in  double  shear,  78,750  Ibs.; 
Then  7X0.375X60,000  =157,500  =  strength  of  solid  plate; 

(7- 0.8125)  X 0.375X60,000  =139,219  =  strength  of  net  section 

of  plate; 
0.5185X4X78,753=  163,327  =  strength    of    four      rivets    in 

double  shear; 
0.5185X45,000  =  23,333  =  strength   of    one    rivet    in    single 

shear; 
163,327  +  23,333  =  186,660  =  shearing     strength     of    all     five 

rivets. 

Net  section  of  plate  is  the  weakest,  and  efficiency  is  88.4%. 
This  style  of  joint  is  much  used  on  the  longitudinal  seams  of 
large  boilers  made  of  heavy  plates. 

Many  engineers  prefer  to  modify  the  above  methods  by  making 
an  allowance  for  the  increase  in  strength  of  plate  between  perfora- 
tions over  that  of  the  plain  plate.  This  increase  is  similar  to  that 
found  in  short  test  specimens  over  long  ones.  It  varies  from  per- 
haps 5  per  cent  to  over  20  per  cent,  and  depends  on  the  length 
between  holes  and  on  the  thickness.  How  much  of  this  increase  can 
be  fairly  trusted  in  a  long  seam  is  doubtful,  due  to  possible  unfair- 
ness in  matching  holes,  and  to  the  unequal  loads  on  the  rivets. 

Many  boilermakers  determine  the  pitch  by  trial,  using  the  fol- 
lowin?;  formula: 


*  Because  the  net  strength  of  plate  is  between  the  outer  row  of  rivets.    If 
not,  the  outer  row  has  to  shear  with  the  breaking  of  plate  between  inner  row. 


222  STEAM-BOILERS 

(a).     —  =  percentage  of  strength  of  plate  at  joint,  as 

compared  to  solid  plate ; 
percentage  of  strength  of  rivet,  as  compared 

to  solid  plate; 

in  which  A  denotes  area  of  one  rivet-hole  in  square  inches ; 
d  diameter  of  rivet-holes  in  inches ; 

p        "       pitch  or  distance  between  centres  of  holes  in 

inches  ; 

t       "       thickness  of  plate  in  inches; 
N      "       number  of  rivets  sheared; 
C  1.00  for  single  shear  and  1.75  for  double  shear. 

Since  the  shearing  strength  of  rivet  cannot  be  taken  as  equal  to 
the  tensile  strength  of  plate,  and  also  since  the  holes  are  not  always 
drilled  fair  and  true,  it  is  found  best  to  so  design  the  joint  that  the 
percentage  of  rivet  strength  should  exceed  that  of  plate  at  joint  in 
about  the  following  proportions: 

For  iron  rivets,  as  12  to  8; 
For  steel  rivets,  as  28  to  23. 

In  other  words,  the  result  of  equation  (6)  to  that  of  equation  (a) 
should  be  in  about  the  above  proportion. 

The  size  of  rivet  should  depend  upon  the  thickness  of  plate,  al- 
though practice  has  become  more  or  less  uniform  in  the  use  of  cer- 
tain sizes  for  different  plates.  No  doubt  higher  efficiencies  would 
be  obtained  by  using  larger  rivets  in  the  thicker  plates  than  are 
commonly  adopted.  Boiler-rivets  are  seldom  used  of  larger  size 
than  1£  inches  in  diameter,  owing  to  the  difficulty  of  driving  them. 
American  practice  rarely  uses  rivets  between  the  even  £  inch  in 
diameter,  although  foreign  builders  adopt  the  intermediate  sizes 
varying  by  y1^  inch,  a  practice  which  has  much  to  commend  it. 

It  is  always  most  convenient  for  manufacturing  reasons  to  design, 
whenever  possible,  all  joints  in  the  boiler  with  the  same-sized  rivets. 

Table  XVIII  represents  about  the  average  practice  of  boiler- 
shops,  showing  the  size  of  rivet  and  pitch.  When  iron  rivets  are 
used,  the  pitch  can  be  reduced.  The  figures  have  been  adopted  for 
simplicity  and  uniformity,  rather  than  for  producing  the  strongest 
possible  combination.  The  low  efficiency  in  some  cases  is  probably 


BOILER   DETAILS 


223 


more  than  offset  by  the  decrease  in  risk  of  ruining  a  plate  by  incorrect 
drilling,  which  might  occur  in  a  shop  if  no  standard  were  adopted. 


TABLE  XVIII 

DETAILS    OF   RIVETED    JOINTS 


Single-riveted 

Double-riveted 

Lap-  Joint. 

Thick- 

Diame- 

ness of 
Plate. 

ter  of 
Rivet. 

Spac- 

Lap-joint. 

Double-strap  feutt. 

Pitch. 

Efficiency. 

ing. 

Pitch. 

Efficiency. 

Pitch. 

Efficiency. 

1 

i 

If 

54.0% 

1 

If 

67.9% 

21 

76.6% 

I 

If 

54.6% 

H 

2t 

67.6% 

2f 

75.3% 

I* 

I 

l| 

55.3% 

H 

2* 

67.5% 

3 

73.0% 

if 

2 

51.7% 

it 

2f 

69.0% 

3, 

?y 

72.7% 

*^ 

1 

2 

51.7% 

i| 

21 

67.2% 

3i 

72.2% 

i! 

2£ 

50.8% 

it 

3 

66.6% 

3^ 

73.6% 

c 

if 

2* 

47.1% 

H 

3 

62.8% 

3: 

73.4% 

if 

2t 

41.6% 

it 

3 

57.2% 

31 

73.3% 

1 

2f 

37.4% 

2 

3i 

57  ^3% 

4 

72.8% 

if 

i 

21 

34.4% 

2 

3t 

52:4% 

4 

71.5% 

i 

,2f 

31.8% 

2 

49.0% 

4 

66.5% 

11 

ITS 

32.0% 

2t 

3| 

47.2% 

41 

65.6% 

i 

1* 

2! 

30.0% 

2i 

3* 

47.4% 

4^ 

64.6% 

iiV 

11 

21 

28.2% 

31 

44.6% 

4^! 

60.8% 

Note.  This  table  shows  the  necessity,  when  using  thick  plates,  of  double 
riveting  lap-joints  and  of  treble-riveting  double-strap  butt-joints,  in  order  to 
secure  high  efficiencies. 

The  efficiencies  were  calculated  by  the  author  on  the  assumption 
of  steel  plate  with  tensile  strength  of  60,000  Ibs.,  steel  rivets  with 
shearing  strength  of  45,000  Ibs.  for  single  and  78,750  Ibs.  for  double 
shear,  and  rivet-holes  TV  inch  larger  than  rivet. 

The  distance  from  edge  of  plate  to  centre  of  first  row  of  rivets 
should  be  one  and  one-half  diameters  of  rivet. 

The  width  of  lap  for  single-riveting  should  be  three  diameters 
of  rivet. 

The  width  of  lap  for  double-riveting  should  be  five  diameters  of 
rivet. 

The  width  of  single-riveted  butt-strap  should  be  six  diameters  of 
rivet. 

The  width  of  double-riveted  butt-strap  should  be  ten  diameters 
of  rivet. 

A  single  butt-strap  must  not  be  less  than  the  thickness  of  the 
plate. 


224  STEAM-BOILERS 

A  double  butt-strap  must  not  be  less  than  five-eighths  the  thick- 
ness of  plate. 

When  plates  of  unequal  thickness  are  to  be  joined,  then  the 
thickness  of  the  thinnest  plate  should  be  used  to  determine  the 
variable  dimensions,  such  as  diameter  of  rivet,  spacing  back  from 
edge,  thickness  of  butt-strap,  etc. 

It  is  at  times  necessary  to  have  a  butt-strap  on  a  surface  that 
is  supported  by  stay-bolts,  and  such  cases  are  more  'or  less  difficult 
to  design.  The  Bigelow  Boiler  Company,  of  New  Haven,  Conn., 
adopts  a  form  shown  in  Fig.  84  for  the  water-legs  of  some  of  their 


Q 

Q 

0   Q 

Q    Q    Q 

Q   Q 

Q 

Q 

Q   Q 

Q 

Q 

Q 

Q   Q 

000 

©   G 

»   0 

0 

0   0 

•== 
0 

FIG.  84. — Butt-strap  on  a  Stayed  Sheet. 

upright  tubular  boilers.  A  form  of  triple-riveted  butt-joint  with 
unequal  straps  is  shown  in  Fig.  85,  taken  from  The  Locomotive,  May, 
1898.  The  stay-bolts  are  shown  in  black.  From  an  experiment 
made  by  the  Bigelow  Company  and  the  Hartford  Steam  Boiler  and 
Insurance  Company,  described  in  the  issue  of  The  Locomotive 
mentioned,  the  conclusion  was  drawn  that  it  was  not  necessary, 
except  in  special  cases,  to  provide  a  triple-riveted  butt-joint  on  the 
outer  sheet  of  a  curved  and  properly  stayed  water-leg. 

Fig.  86  illustrates  a  design  for  a  triple-riveted  butt-strap. 

Welding.  Boiler-sheets  have  been  joined  by  welding.  Al- 
though only  used  to  a  limited  extent,  this  method  has  many  prom- 
ising advantages.  The  principal  objection  is  the  cost. 

The  strength  of  the  weld   v:hen  well  done,  appears  to  be  equal 


BOILER  DETAILS  225 

to  that  of  the  sheet,  but  always  cannot  be  relied  upon.  For  making 
domes,  cylinders  for  storing  gases  under  heavy  pressures,  and  for 
special  shapes,  welding  has  been  very  successful. 

The  welding  may  be  accomplished  by  the  use  of  an  electric 
current  or  by  heating  the  edges  and  pressing  them  together. 
This  is  generally  done  by  passing  the  part  to  be  welded  between 
rollers.  Lest  the  plates  should  stretch  under  the  latter  opera- 


FIG.  85. — Double-riveted  Butt-strap  of  Unequal  Width  on  a  Stayed  Sheet. 

tion,  they  should  be  welded  first  at  the  centre  and  then  at  the 
ends,  the  intermediate  portion  being  welded  afterward.  Cor- 
rugated and  similar  forms  of  flues  and  boiler-tubes  are  always  lap- 
welded.  Electric  welding  is  done  by  the  use  of  an  alternating 
current  of  low  voltage,  generally  not  exceeding  three  volts,  and  of 
large  volume. 

The  edges  should  be  slightly  upset  or  thickened  and  bevelled, 
and  be  heated  on  both  sides  at  once.  The  pieces  may  be  heated 
in  a  special  gas-furnace,  using  a  mixture  of  2J  volumes  of  air 
to  one  volume  of  hydrogen  or  water  gas.  The  use  of  a  "glut" 


226 


STEAM-BOILERS 


piece  is  discarded  as  unnecessary  and  as  only  extending  the  sur- 
face of  the  weld. 

A  general  use  of  welding  for  boiler  shells  subject  to  tension 
has  been  prevented  by  the  irregular  strengths  of  the  welds,  the  effi- 
ciency varying  from  about  50  per  cent  to  100  per  cent.  Steel  can- 
not be  always  successfully  welded,  which  is  true  unless  the  material 
be  mild.  The  danger  of  the  use  of  a  sheet  that  will  not  weld,  the 

DOUBLE  BUTTSTRAP 


THICKNESS  11/,6 

SHELL  1'/'i6 

RIVETS  11/s 

STEAM   PRESSURE  150  LBS. 


1  —  f.                          f                           ~ 

o 

000 
000 

000 

ooo 
o 

o 
o 

0 

c 

o        o 

0           C 

O           ( 
0           0 
( 

o        o  •       o        o        o 

5            O       •     O            O            O 

)                          O                          C1 

N^ 

20  SPCS 

OF  2V"  =  3'  9" 

FIG.  86. — Design  for  a  Triple-riveted  Butt-strap. 

formation  of  a  coating  of  oxide,  and  the  failure  to  show  visible 
evidence  of  defect  must  always  carry  great  weight  against  weld- 
ing as  at  present  practised. 

Setting.  Boilers  of  all  types  should  be  set  on  a  firm  founda- 
tion so  as  to  prevent  unequal  settling.  They  always  should  be 
located  in  dry  places. 

Most  boilers  are  set  in  brickwork,  although  some  of  the  water 
tubular  types  are  encased  in  sheet  iron  or  steel,  and  a  few  special 
designs,  as  the  upright  or  vertical  boilers,  require  no  setting  beyond 
the  foundation. 

However  set,  all  boilers  must  be  allowed  ample  freedom  for 
expansion  and  contraction,  lest  the  setting  be  seriously  damaged. 
The  brickwork  is  often  laid  so  close  to  the  shell  that  the  rivet-heads 
are  encased.  When  expansion  takes  place,  some  of  the  bricks  are 
dislodged.  On  contracting  again,  dirt  settles  in  the  newly  made 
opening,  and  the  process  is  repeated  until  the  setting  is  badly 
cracked. 

Good  hard-burned  bricks  should  be  used,  set  in  strong  mortar. 
The  brickwork  should  not  touch  the  boiler,  as  the  bricks  are  hydro- 
scopic  and  retain  moisture  for  a  long  time,  thus  rendering  the 


BOILER   DETAILS  227 

boiler  liable  to  corrosion  at  a  place  not  easily  seen.  A  better  plan 
is  the  filling  of  all  spaces  between  the .  boiler  and  the  masonry 
with  asbestos  and  fire-clay. 

The  setting  of  each  boiler  should  be  designed  for  its  particular 
kind  and  location,  but  a  few  general  hints  may  not  be  out  of  place. 
The  setting  should  have  more  attention  given  to  it  than  is  usually 
done,  and  less  reliance  placed  on  the  mason,  who  has  little  interest 
at  stake.  Considerable  quantities  of  air  filter  through  even  good 
brickwork,  which  materially  damages  the  draft  and  general  effi- 
ciency. All  doors  and  other  openings  should  have  good  cast-iron 
frames,  so  set  in  the  wall  as  to  be  practically  airtight  between 
frame  and  bricks.  The  doors  should  fit  snug.  Since  the  draft  is 
always  inward,  the  leakage  is  not  readily  visible  or  determinable. 
It  is  a  good  practice  to  paint  the  brick  setting  with  some  heavy 
tar  paint. 

The  brick  walls  are  best  made  double  with  an  air  space  of  2 
inches  between  them.  These  walls  can  be  tied  across  at  intervals 
by  headers.  A  very  good  plan  is  to  make  the  outer  wall  12J  inches 
thick  and  the  inner  wall  8  inches  with  an  air  space  of  4  inches. 
The  headers  in  the  outer  wall  project  across  the  air  space  and 
simply  touch  the  inner  wall,  but  are  not  tied  to  it.  This  arrange- 
ment permits  the  two  Avails  to  expand  at  will  without  injury  to  each 
other,  while  the  headers  lend  support  to  the  inner  one. 

The  joints  should  be  about  j-inch  thick.  The  mortar  is  fre- 
quently of  lime,  but  should  be  of  hydraulic  cement,  or  one  part 
cement  to  three  parts  lime.* 

When  single  walls  without  an  air  space  are  used,  they  should 
be  two  bricks  or  174  inches  thick,  exclusive  of  lining.  When 
boilers  are  set  in  battery,  the  partition  or  division  walls  need  be 
only  124  inches  in  thickness.  The  outer  walls  are  tied  together 
by  tie-rods  about  one  inch  in  diameter  and  fastened  to  binder 
bars  or  brick  staves.  These  binder  bars  are  generally  made  of  cast- 
iron  with  a  tee  section,  having  the  greatest  depth  at  the  centre. 
The  ends  of  the  walls  should  be  exposed,  so  that  any  bulging  may 
be  quickly  noticed. 

The  inside  of  the  brickwork  exposed  to  the  direct  action  of  the 
heat  should  be  of  fire-brick  4  inches  or  44  inches,  according  to 
the  size  of  brick  used,  and  be  set  in  fire-clay.  If  any  trimming  has 
to  be  done,  trim  the  red  bricks  in  preference  to  the  fire-bricks. 
This  fire-brick  lining  should  be  arranged  independent  of  the 

*  The  lime  makes  the  cement  work  more  smoothly  and  sot  more  slowly. 


228  STEAM  BOILERS 

regular  brick  setting,  so  that   it  may  be  renewed  without  neces- 
sitating the  taking  down  of  the  latter. 

The  tops  of  many  externally  fired  boilers  are  cohered  with  a 
brick  arch  resting  on  the  side  walls.  This  is  not  a  good  plan,  as 
leaks  may  occur  and  not  be  noticed.  A  better  plan  is  to  cover 
the  top  with  sectional  covering  blocks  laid  touching  the  boiler, 
so  that  if  a  leak  occurs  a  wet  spot  will  show;  or  with  sand  which 
can  be  brushed  aside  for  inspection.  To  prevent  the  sand  running 
out,  the  joint  between  the  shell  and  the  setting,  which  is  liable 
to  open  by  expansion,  should  be  filled  with  asbestos  and  be  covered 
with  sheets  of  asbestos  paper  well  lapped. 

Scotch  boilers  do  not  require  a  brickwork  setting.  They  rest 
on  saddles  placed  on  suitable  foundations.  In  ships  these  saddles 
are  either  of  steel  plates  or  of  cast-iron,  or  are  formed  by  extending 
upward  the  ship's  floors  and  riveting  double  angles  on  the  tops, 
curved  to  fit  the  shell.  In  stationary  work  the  saddles  are  nearly 
always  of  cast-iron.  In  length  they  should  be  not  less  than  one- 
third  the  diameter  of  shell  and  about  5  to  7  inches  in  width. 
Ordinarily  two  saddles  are  sufficient;  and  three  should  only  be 
used  with  great  care,  owing  to  the  difficulty  of  keeping  these  points 
in  alignment,  so  as  to  divide  the  load.  When  the  saddles  are 
large  they  may  be  made  in  halves  and  bolted  together.  When 
boilers  are  rested  on  metallic  supports  it  is  customary  to  place 
red  lead  or  putty  on  the  supports,  in  order  that  an  even  surface 
may  be  insured.  It  should  be  used  thick,  so  that  the  boiler  may 
squeeze  it  down  to  a  proper  bearing.  Pure  white-lead  putty,  well 
mixed  with  a  good  oil,  is  much  better  than  red  lead,  as  the  latter  gets 
hard  and  brittle  and  chips  out.  The  boiler  need  not  be  fastened 
to  the  saddles,  as  its  weight  is  sufficient.  On  shipboard  the  boiler 
must  be  tied  down  both  vertically  and  fore  and  aft,  to  prevent 
dislodgement  due  to  rolling,  pitching  or  collision.  The  size  of 
these  steel  tie-pieces  cannot  be  calculated,  but  are  made  to  suit 
the  conditions  and  judgment  of  the  designer. 

It  is  often  convenient  to  estimate  the  approximate  number  of 
bricks  required  for  the  setting  of  a  horizontal  return-tubular  boiler, 
and  the  accompanying  table,  taken  from  Locomotive,  November, 
1891,  will  be  found  useful. 

Bridge  Wall.  At  the  back  end  of  the  grate  a  bridge  wall  is 
formed  so  as  to  prevent  the  coal  from  falling  off,  and  to  compel  the 
draft  to  pass  upward  through  the  grate  and  bed  of  coal. 


BOILER   DETAILS 


229 


TABLE  XIX 

NUMBER    OF    BRICKS    IN    BOILER    SETTINGS 


c 

*""* 

c 

"~* 

*o.S 

'ofcfc   . 

(4 

(_<  rz3  O<  QO 

1 

1 

5  -a 

£0 

Number  of 

|«f| 

m 

3 

Common 

3  C  *~  ^ 

r—i 

H 

Kind  of 

Number  of 

Number  of 

fa 

Brick  for 

^  W      o 

O 

IM 

Front. 

Common 

Fire-brick. 

T5  ® 

Each  Boiler 

»     • 

o 

Brick. 

C  a  rj 

After  the 

c<5'5  § 

•sj 

•G    . 

.9  >>  •*= 

First. 

.2_^  ^  (^ 

ll 

1| 

•S.2  c 

|ll-i 

36 

10 

Flush 

11,700 

564 

660 

6,300 

350 

36 

10 

Overhanging 

11,000 

525 

660 

5,900 

350 

42 

12 

Flush 

13,700 

654 

680 

7,400 

360 

42 

12 

Overhanging 

13,000 

629 

680 

7,000 

360 

48 

15 

Flush 

16.700 

850 

710 

8,900 

370 

48 

15 

Overhanging 

16,000 

816 

710 

8,500 

370 

54 

15 

Flush 

17,600 

990 

730 

9,400 

380 

54 

15 

Overhanging 

16,700 

886 

730 

8,900 

380 

60 

16 

Flush 

19,100 

1,140 

760 

10,200 

400 

60 

16 

Overhanging 

18,200 

950 

760 

9,700 

4CO 

66 

16 

Flush 

21,900 

1,290 

830 

11,900 

450 

66 

16 

Overhanging 

20,600 

1,080 

830 

11,300 

450 

72 

18 

Flush 

24,000 

1,400 

860 

13,400 

460 

72 

18 

Overhanging 

23,000 

1,150 

860 

12,800 

460 

In  externally  fired  boilers  the  wall  is  built  of  brick  lined  on 
the  fire  side  and  top  with  fire-brick.  In  internally  fired  boilers 
the  wall  is  usually  made  of  two  or  three  pieces  of  special-shaped 
fire-brick  cemented  with  fire-clay,  or  of  ordinary  fire-brick  and 
fire-clay. 

The  shape  of  the  wall,  whether  flat  on  top  or  curved  to  corre- 
spond with  round  of  shell,  with  vertical  or  with  sloping  sides,  appears 
to  make  little  difference,  according  to  tests  made  by  George  H. 
Barrus.  The  area  over  the  wall  must  be  large  enough  so  as  not  to 
check  the  draft,  while  beyond  that  the  effect  of  shape  appears  to 
be  slight.  A  flat  wall  is  easier  to  build,  but  most  engineers  prefer 
a  curved  top  and  a  vertical  front  face,  with  the  upper  edge  cut 
away  at  an  angle  of  45  degrees. 

With  soft  and  hydrocarbonaceous  coals  it  is  best  to  admit  some 
air  above  the  grate,  and  for  that  purpose  the  bridge  wall  is  often 
made  "split,"  that  is,  hollow,  with  air-passages  in  its  back  face  or 
on  top.  These  passages  or  holes  may  be  made  in  a  cast-iron  plate 
set  in  the  bridge  wall,  or  be  made  between  the  bricks  by  spacing 
them  a  short  distance  apart.  The  hollow  centre  of  the  wall  can  be 
connected  to  the  air  space  in  the  side  walls  of  setting,  so  as  to 


-20  STEAM-BOILERS 

draw  heated  air  only.  The  air-supply  should  be  easily  control'ed 
by  a  damper.  In  internally  fired  flues,  air  may  be  passed  from  the 
ash-pit  through  an  opening  in  the  plate  beneath  the  bridge  wall, 
which  opening  can  be  controlled  by  a  slide  or  damper  door,  easily 
moved  by  the  slice-bar  or  poker  from  the  front.  (Figs.  124 
and  125.) 

The  split  bridge  often  materially  assists  in  preventing  the  gen- 
eration of  an  excess  of  smoke,  but,  like  every  other  device,  must  be 
intelligently  handled. 


CHAPTER  IX 
BOILER  FITTINGS 

Mountings  and  Gaskets.  Steam-dome.  Steam-drum.  Steam-super- 
heater. Steam-chimney.  Steam-pipe.  Stop-valve.  Dry  Pipe.  Boiler- 
feed.  Injector  and  Pump.  Feed-water  Heater,  Purifier,  and  Economizer. 
Filters.  Mud-drum.  Blow-off.  Bottom  and  Surface  Blows.  Safety-valve. 
Fusible  Plug.  Steam-gauge.  Water-gauge.  Try-cocks.  Water-alarm. 
Man-hole  and  Hand-hole.  Grates,  Stationary  and  Shaking.  Down-draft 
Grates.  Ash-pit.  Fire-doors.  Breeching.  Uptake.  Smoke  Connection. 
Draft  Regulator.  Steam-traps.  Separators.  Evaporators. 

IN  placing  the  mountings  of  a  steam-boiler,  care  must  be  taken 
to  insure  a  tight  joint  and  one  that  will  remain  so  under  the  trying 
stresses  of  usage.  Many  boilers  have  undoubtedly  failed,  while 
otherwise  amply  strong,  due  to  carelessness  in  this  regard. 

There  is  little  trouble  on  flat  parts,  since  the  flange  of  the  mount- 
ing can  be  faced,  and  bolted  or  riveted  direct  to  the  sheet.  It  is 
well  to  place  between  the  flange  and  the  plate  either  cement  or 
a  gasket  of  fine-brass  wire  netting  set  in  red-lead  putty.  The 
flange  must  be  heavy  enough  to  allow  the  nuts  to  be  screwed  up 
hard,  and  these  bolts  must  not  be  spaced  too  far  apart  lest  the 
joint  be  apt  to  leak.  The  bolts  should  not  be  spaced  farther  than 
seven  thicknesses  of  the  plate  or  flange,  whichever  is  the  thinner. 
The  nut  should  be  screwed  down  on  a  grummet  of  cement,  or  cot- 
ton waste,  or  lamp-wi eking  mixed  with  red-lead  cement.  It  is 
best  to  face  off  the  base  of  the  nut  and  turn  a  shallow  groove  so  as 
to  hold  the  packing. 

On  the  curved  surfaces  of  the  shell  or  dome  the  mounting  may 
be  placed  on  a  seating  riveted  to  the  plate.  This  seating  can  be 
made  curved  to  truly  fit  the  plate,  and  flat  to  fit  the  flange  of 
mounting;  and  can  be  calked  against  the  plate  both  on  inside 
and  outside  of  shell. 

Small  pipes  may  be  screwed  into  the  shell-plates,  but  it  is  well 
to  have  a  flange  in  all  cases.  When  a  flange  is  not  convenient,  a 

231 


232 


STEAM-BOILERS 


thickening  plate  may  be  riveted  to  the  plate  and  both  tapped  for 
the  pipe  thread. 

Corrugated-copper  gaskets  will  be  found  very  serviceable  for 
making  large  joints,  especially  for  those  which  have  to  be  occa- 
sionally taken  apart.  Hard-rubber  gaskets  are  frequently  used ; 
and,  at  times,  copper  wire  or  small  lead  pipe  laid  in  a  groove  in 
the  flange  and  pressed  tight  when  the  bolts  are  set  up,  will  prove 
satisfactory.  This  groove  must  be  on  the  pressure  side  of  all  bolt- 
holes. 


FIG.  87. — Steam-dome. 


Steam-domes  are  common  appendages  to  the  ordinary  boiler, 
but  are  gradually  being  discarded.  They  serve  to  increase  the 
steam  space  and  permit  dry  steam  to  collect  at  a  point  high  above 
the  water-line,  whence  it  may  be  drawn  off  by  the  engine.  As  a 
matter  of  fact,  their  usefulness  for  this  purpose  is  rather  more 


BOILER  FITTINGS 


233 


imaginary  than  real.  As  usually  constructed,  they  are  not  suffi- 
ciently large  to  materially  affect  the  steam  room,  and  a  few  strokes 
of  the  engine  will  exhaust  them.  Also,  judging  by  the  mud  and 
scale  that  often  accumulates  within,  they  are  of  little  aid  in  furnish- 
ing dry  steam.  A  dry  pipe  or  steam-collecting  pipe  may  be  used 
to  better  advantage. 

Domes  weaken  the  shell,  due  to  the  large  hole  that  has  to  be 
cut  out  (Fig.  87).  The  shell  should  be  strengthened  at  that  point, 
although  the  strength  due  to  the  flanging  and  fastening  of  the  dome 
is  usually  relied  upon.  When  large  domes  are  used,  it  is  only 
necessary  to  cut  a  hole  in  the  shell  large  enough  for  a  man  to  pass 
through,  and  let  the  dome  attach  back  from  the  edge.  The  edge 
of  the  hole  should  be  stiffened  the  same  as  if  for  a  manhole.  The 
objection  to  this  plan  is  the  formation  of  a  shelf,  caused  by  the 
projecting  sheet  of  the  shell,  on  which  water  and  mud  will  collect. 
This  projection  of  the  shell  should  be  perforated  so  as  to  drain, 
but  even  so,  the  drainage  is  not  effectual.  If  the  hole  at  the  centre 
for  steam  be  too  small,  there  will  be  a  tendency  to  prime. 

The  top  of  the  dome  can  be  made  out  of  one  sheet,  and  be 
flanged  to  meet  the  shell  of  the  dome,  having  the  lap  on  the  inside. 
This  top  can  be  bumped  so  as  to  be  self-supporting,  being  made  as 


FIG.  88. — Steam-drum,  Single  Nozzle. 

part  of  the  surface  of  a  sphere  whose  diameter  is  twice  that  of  the 
dome.  If  the  top  be  flat  it  will  require  staying.  Often  a  man- 
hole is  placed  on  top  of  the  dome,  and  in  such  cases  the  steam-pipe 
leads  from  the  side. 


234 


STEAM-BOILERS 


A  Steam-drum  is  better  than  a  dome  for  increasing  the  steam- 
space,  as  it  can  be  larger  than  the  ordinary  dome  and  requires  less 


FIG.  89. — Steam-drum,  Double  Nozzle. 

cutting  of  the  boiler-shell  (Figs.  88,  89,  and  90).  The  drum  is 
designed  according  to  the  same  principles  that  apply  to  the  shell. 
It  consists  of  a  cylindrical  vessel  having  a  diameter  about  half 
of  that  of  the  boiler-shell  or  less.  The  heads  are  most  always 
bumped,  with  a  manhole  in  one  of  them.  It  is  connected  to 
the  shell  by  a  neck  or  nozzle,  which  is  made  of  riveted  steel, 


FIG.  90. — Steam-drum,  Pipe  Connection. 

welded  steel,  or  more  commonly  of  cast-steel  or  cast-iron.  When 
cast  they  are  generally  proportioned  according  to  the  standard 
sizes  illustrated  in  Fig.  91. 

The  drum  may  be  arranged  as  in  Fig.  88,  with  one  nozzle,  or  as 
in  Fig.  89,  with  two  nozzles.    This  latter  method  is  objectionable 


BOILER  FITTINGS 


235 


on  the  ground  of  unequal  expansion.  If  the  drum  be  so  long  and 
heavy  as  to  require  two  supports,  it  is  better  to  have  a  nozzle  at 
one  end  and  a  false  nozzle  or  saddle  at  the  other. 

Sometimes  one  drum  is  common  to  two  or  three  boilers,  and  is 
then  placed  at  right  angles  to  the  boiler  axes ;  but  this  arrangement, 


USUAL  DIMENSIONS  -  INCHES 


A 

1O 

1  1 

12 

B 

4 

5 

6 

C 

6 

7 

8 

D 

8'/2 

9}'2 

10  '/2 

E 

1  1 

12 

13 

f 

6 

6 

6 

FIG.  91. — Standard  Nozzles  of  Cast-iron  or  Cast-steel. 

while  convenient,  is  difficult  to  maintain,  due  to  the  stresses  caused 
by  differences  in  expansion,  and  prevents  the  use  of  one  boiler 
without  the  other  unless  a  stop- valve  is  interposed.  It  is,  there- 
fore, most  serviceable  in  large  batteries. 

The  drum  forms  a  very  essential  part  in  the  design  of  most 
water-tubular  boilers. 

A  Steam-superheater  is  a  large  steam-drum  through  which  a 
flue  passes,  conveying  the  products  of  combustion  from  the  boiler 
to  the  uptake  or  stack.  They  are  misnamed,  as  they  are  not 
designed  primarily  to  superheat  the  steam,  lacking  sufficient 
heating  surface  to  be  effective.  They  are  made  in  various  styles, 
some  of  which  are  illustrated  in  Figs.  26  and  27.  They  are  usually 
supported  on  the  shell  of  the  boiler  in  such  a  manner  that  the 
weight  of  the  superheater  is  carried  by  its  flue.  The  adoption  of 
outside  stays  between  the  shells  of  superheater  and  boiler  are  not 
to  be  recommended,  as  they  frequently  are  sources  of  trouble  from 
unequal  expansion. 

The  steam  pipe  from  the  boiler  should  enter  at  the  side  of 


236 


STEAM-BOILERS 


the  superheater,  although  it  may  enter  the  bottom.  In  the 
former  case  there  should  be  a  small  drain  from  the  bottom  of 
the  superheater  back  to  the  boiler.  This  drain  is  generally  made 
of  seamless  drawn  copper  pipe,  from  2  inches  to  4  inches  in  diam- 
eter, according  to  requirements,  but  the  smaller  the  better,  and  it 
should  be  curved  for  expansion.  This  drain  should  enter  the 
boiler-shell  just  below  the  water-line,  and  no  check-valve  is  re- 
quired unless  a  great  difference  in  pressure  is  expected. 

A  manhole  should  be  worked  in  at  some  convenient  place, 
and  usually  the  upper  head  is  selected. 

The  flue,  or  liner  as  it  is  called,  may  be  made  of  one  flue  or  of 
a  number  of  smaller  ones  as  desired.  These  liners  are  proportioned 
according  to  the  rules  for  a  flue  subjected  to  external  pressure,  but 
with  a  large  factor  of  safety,  as  it  is  all  superheating  surface  and 
exposed  to  high  temperatures.  The  United  States  Steamboat 
Inspection  Rules  for  liners  are  given  under  Flues,  Chapter  VIII. 
When  a  heavy  stop-valve  is  placed  on  the  side  of  a  superheater 
or  steam-chimney,  the  joint  is  apt  to  leak  and  cause  trouble,  unless 

the  valve  be  securely  supported  and 
braced.  The  flange-bolts  do  not  have 
sufficient  leverage  to  resist  the  continual 
vibration  caused  by  the  engine  shaking 
the  steam-pipe.  The  valve  can  often  be 
supported  by  long  flat  or  angle  braces, 
leading  from  the  outer  flange  to  points 
higher  up  on  the  shell,  as  in  Fig.  92. 

A  Steam-chimney  is  a  steam-dome 
of  large  size,  through  which  the  smoke- 
flue  passes,  as  in  Fig.  25.  It  necessarily 
weakens  the  shell  by  cutting  out  so 
large  a  piece,  and  has  all  the  disadvan- 
tages of  the  dome,  without  any  addi- 
tional advantages  over  the  ordinary 
forms  except  that  of  size. 

Steam-chimneys  are  seldom  used  ex- 
cept on  " marine"  type  of  boilers  designed  for  steam  pressures  of 
40  pounds  on  the  inch  or  less.: 

Steam  domes,  drums,  superheaters  and  chimneys  are  but  make- 
shifts when  used  for  increasing  the  steam-space,  and  are  best 
avoided  whenever  possible. 


FIG.  92. — Angle     Braces 
Support  Stop-valve. 


to 


BOILER  FITTINGS  237 

Steam-pipes  should  be  of  such  size  that  the  average  velocity 
of  flow  does  not  exceed  about  8000  feet  per  minute.*  The  area 
through  valves  should  be  somewhat  in  excess  of  that  of  the  pipe,  so 
as  not  to  create  loss  of  pressure  due  to  friction. 

The  steam-pipe  leading  from  a  boiler  may  cause  priming  if 
made  too  large.  A  rule  for  size  of  steam-pipe  to  suit  a  boiler,  as 
stated  by  Seaton  in  Manual  of  Marine  Engineering,  is  that  the 
area  should  not  exceed  the  following: 

Area  in  square  inches  =  (0.25 X  grate  area  in  square  feet-f  0.01 
X  heating  surface  in  square  feet)  X 

100 


Pressure  in  pounds  per  square  inch. 

In  cases  where  a  steam-drum  or  superheater  is  used,  the  steam- 
room  in  the  boiler  proper  is  generally  small  for  the  engine,  and, 
further,  the  engine  is  apt  to  be  of  the  early  cut-off,  long-stroke, 
slow-speed  type.  The  greater  care  should  then  be  taken  to  see 
that  the  pressure  does  not  vary  too  much  in  the  boiler  at  each  gulp 
of  steam  taken  by  the  engine.  The  steam-pipe  between  the 
boiler  and  the  drum  or  superheater  must  not  be  made  too  large. 
It  may  be  as  large  as  that  leading  to  the  engine  but  not  larger,  or 
it  may  even,  with  good  result,  be  made  somewhat  smaller.  The 
area  should  not  exceed  that  given  by  Seaton's  rule,  and,  according 
to  circumstances,  should  often  be  much  less.  When  the  steam 
is  taken  by  gulps  at  long  intervals,  the  drum  or  superheater  may 
act  like  a  reservoir;  and  changes  of  pressure  occurring  in  it  will 
cause  a  more  or  less  steady  flow  from  the  boiler. 

If  wet  steam  is  expected,  a  steam  separator  on  the  steam-pipe 
near  the  engine  is  recommended.  A  separator  is  a  safeguard  in 
every  case,  as  it  will  prevent  a  possible  accident  to  the  engine  from 
water,  whether  the  water  comes  from  priming,  condensation, 
carelessness  or  otherwise,  and  it  also  will  act  as  a  steam-reservoir. 

Pipes  must  be  strong  enough  to  withstand  the  required  pres- 
sure. Wrought-iron  and  steel  pipes  are  made  amply  strong  for 
all  reasonable  pressures,  on  account  of  the  thickness  necessitated 
by  conditions  of  manufacture.  For  copper  pipes,  the  British 
Board  of  Trade  rule  may  be  safely  taken  as  a  minimum;  namely, 
for  copper  steam-pipes,  when  brazed, 


Thickness  in  inches  =  +     , 


*  In  large  pipes,  the  velocity  may  be  16,000  feet. 


238  STEAM-BOILERS 

and  when  seamless,  not  exceeding  8  inches  in  diameter. 


Thickness  in  inches  =  +      , 


in  which 

p  denotes  working-pressure  in  pounds  per  square  inch,  and 
d  denotes  inside  diameter  in  inches. 

Long  bends  should  be  made  one  gauge  thicker  than  the  straight 
parts  and  short  bends  two  gauges  thicker,  as  the  material  at  the 
back  is  thinned  by  bending.  The  result  is  that  the  bend  is  of  un- 
equal thickness  and  more  rigid  than  necessary,  an  argument  in 
favor  of  as  long  a  bend  as  possible. 

Failures  of  Steam-pipes  are  caused  by  poor  design,  carelessness 
or  neglect,  and  seldom  by  weakness  due  to  the  pipe  having  been 
made  originally  too  thin.  The  majority  of  failures  are  traceable  to 
lack  of  provision  for  expansion  and  contraction,  and  to  the  move- 
ment occasioned  by  the  vibration  of  the  engine.  The  other  princi- 
pal causes  are  lack  of  suitable  means  for  drawing  off  the  watc  r  of 
condensation,  faulty  workmanship,  and  defects  that  have  developed 
while  the  pipe  has  been  in  use. 

Steam-piping  can  be  so  designed  that  ordinary  carelessness  or 
foaming,  of  the  boilers  will  not  cause  an  accident.  The  difference 
in  cost  between  a  good  and  a  bad  design  is  never  large  enough  to 
be  of  any  importance.  Lack  of  sufficient  head  room,  however, 
often  creates  considerable  difficulty  in  laying  out  a  steam-piping 
system,  and  occasionally  prevents  the  designer  from  adopting 
the  best  arrangement. 

The  materials  used  for  steam-piping  are  copper,  wrought-iron, 
'mild  steel  and  cast-iron,  and  the  design  should  conform  to  the 
material  employed. 

Copper  pipes  are  either  brazed  or  seamless-drawn.  Seamless- 
drawn  pipes  can  be  made  as  large  as  8  inches  in  diameter  and 
bends  can  be  worked  by  the  coppersmith  from  straight  pieces. 

Brazing  is  now  usually  made  on  a  lap  seam,  but  formerly  was 
done  by  dove-tailing  the  edges.  When  pipes  are  brazed,  the 
straight  pieces  have  one  seam,  and  bends  of  small  sizes  can  be 
made  from  such  straight  pieces.  Bends  in  large  pipes  are  made  in 
halves  with  two  brazed  seams,  one  on  each  side. 

The  flanges  are  generally  brazed  on,  while  the  end  of  the  pipe 
is  bent  over  into  a  recess  turned  in  the  face  of  the  flange,  to  pre- 


BOILER   FITTINGS  239 

vent  its  being  pulled  out.  At  times  the  flanges  are  riveted  in 
addition  to  the  brazing. 

Copper  was  originally  adopted  for  pipe-making  on  account  of 
its  ductility  and  flexibility.  Its  extended  use  is  now  due  to  cus- 
tom, as  these  properties  are  not  found  to  be  permanent,  but  are 
dependent  upon  the  treatment  of  the  material  while  in  service. 
When  thoroughly  annealed,  copper  is  very  soft  and  takes  a  per- 
manent set  at  pressures  as  low  as  4500  pounds  per  square  inch. 
Its  elongation  will  be  between  30  and  40  per  cent  in  test-pieces  8 
inches  long,  and  its  ultimate  strength  about  28,000  to  30,000 
pounds  per  square  inch.  Under  stress,  often  repeated,  the  copper 
will  harden  and  gradually  have  its  ductility  decreased,  but  may 
be  restored  to  its  original  condition  by  being  annealed.  It  would 
be  advisable  to  periodically  anneal  all  copper  steam-pipes,  but 
this  is  a  difficult  process,  as  very  few  works  are  capable  of  annealing 
a  full  length  of  pipe  at  one  heat,  and  when  done  at  successive  heats 
there  is  danger  of  leaving  parts  hard,  thereby  producing  an  un- 
homogeneous  pipe  which  may  be  worse  than  leaving  it  unannealed. 

Copper  pipes  are  frequently  reinforced  for  additional  security 
when  larger  than  8  inches  in  diameter.  The  reinforcement  not 
only  strengthens  the  pipe,  but  also  greatly  confines  the  place  of 
failure.  It  is  done  by  wrapping  the  pipe  with  copper,  steel  or 
delta-metal  wire,  or  by  fitting  bands  of  wrought-iron  or  other 
suitable  material  at  short  intervals.  The  diameter  of  the  wire  is 
generally  ^-inch  or  T36-inch,  and  is  stretched  on  under  a  tension  of 
about  3000  pounds  per  square  inch  of  section.  It  may  be  wound 
in  spirals  with  closely  laid  coils,  usually  three  wires  being  used  for 
safety;  or  it  may  be  shrunk  on  in  separate  bands  with  the  ends 
twisted.  A  system  of  banding  is  shown  in  Fig.  93  (Marine  Engineer- 
ing, August;  1899).  The  figure  is  self-explanatory,  and  shows 
the  method  of  driving  the  cotters,  as  well  as  of  passing  bends  and 
of  making  a  hub  for  a  branch. 

The  coefficient  of  expansion  of  copper  is  0.00000887  for  each 
degree  Fahrenheit. 

Wrought-iron  and  steel  pipes  are  now  being  largely  used  in  lieu 
of  copper.  When  steel  is  used,  only  the  mildest  qualities  are 
selected.  Wrought  iron  is  preferred  to  steel  by  many  engineers 
on  account  of  the  greater  certainty  of  making  a  strong  welded 
joint. 

In  both  iron  and  steel  pipes  the  joint  is  lap-welded  and  never 


240 


STEAM-BOILERS 


butt-welded,  although  in  small  sizes  the  pipes  can  be  solid  drawn. 
With  steel  pipes,  a  riveted  butt-strap  is  sometimes  fitted  over 
the  weld,  but  if  the  best  material  is  used  and  care  taken  in  making 
the  weld,  this  strap  is  unnecessary.  It  then  only  adds  additional 


METHOD  OF  DRIVING  KEYS 


FIG.  93. — Reinforcing  Steam-pipes. 

cost,  weight  and  numerous  rivet-holes,  which  are  always  liable 
to  leak  and  cause  annoyance. 

Riveted  steel  pipes  are  not  used  to  any  great  extent,  as  they  are 
expensive  and  liable  to  leak  at  the  rivets  and  seam.* 

Iron  and  steel  pipes  are  nearly  always  made  straight,  but  bends 
may  be  made  with  a  radius  of  three  times  the  bore  for  pipes  less 
than  6  inches  in  diameter,  and  four  times  the  bore  for  pipes  as 
large  as  12  inches. 

The  effect  of  corrosion  of  iron  and  steel  pipes  is  not  serious,  as 
thus  far  shown  by  experience. 

The  coefficient  of  expansion  is  0.00000648  for  each  degree 
Fahrenheit,  or  only  two-thirds  that  of  copper. 

Cast-iron  is  seldom  used  for  steam-pipes,  due  to  its  treacherous 
nature,  but  is  used  for  flanges  and  fittings.  The  best  cast-iron  for 
pipe-making  is  charcoal  iron  with  3  per  cent  of  aluminum  to  pre- 

*  Reference  is  made  to  paper  on  "  Riveted  Steel  Pipe,"  with  discussion, 
Trans.  Am.  Soc.  Mechanical  Engineers,  Vol.  XV,  1894. 


BOILER   FITTINGS  241 

vent  blow-holes.  The  coefficient  of  expansion  of  cast-iron  is 
0.00000556  for  each  degree  Fahrenheit. 

A  duplicate  system  is  not  necessary  with  a  well-designed  steam- 
piping  plan.  A  system  in  duplicate  is  expensive,  contains  more 
joints  and  generally  increases  the  condensation.  But  when  used 
the  separate  systems  are  connected  with  "Ys"  at  the  boiler  and 
at  the  engine. 

They  are  arranged  according  to  one  of  three  general  plans,  thus : 

1.  Two  sets  of  mains,  each  of  small  size,  but  of  an  aggregate 
area  to  suit  the  plant.     Both  are  in  use,  but  one  could  be  shut 
down  for  repairs  while  the  other  was  operated  in  times  of  emer- 
gency. 

2.  Two  sets  of  mains,  one  of  full  size  and  one  of  smaller,  the 
smaller  to  be  in  reserve  and  made  small  to  save  cost. 

3.  Two  sets  of  mains,  each  of  full  size,  but  only  one  in  use  at  a 
time.     The  second  main  is  in  reserve. 

The  relative  merit  of  these  plans  is  in  the  order  mentioned, 
unless  some  unusual  condition  exists.  The  first  plan  is  the  cheap- 
est and  strongest,  as  the  pipes  are  of  small  diameter,  and  under 
regular  working  conditions  there  is  no  idle  part. 

In  modern  plants,  duplicate  piping  is  little  used,  and  continued 
experience  confirms  this  view.  Some  electric-lighting  stations 
and  plants  of  similar  character  still  retain  them,  but  there  is  a 
strong  feeling  adverse  to  their  adoption,  on  the  ground  that  they 
are  a  needless  expense  and  increase  the  radiation  surface,  joints, 
valves  and  fittings. 

Ample  allowance  for  expansion  must  be  provided  in  all  steam- 
pipe  designs,  as  most  of  the  failures  that  have  occurred  have 
been  circumferential  fractures  near  the  flanges,  instead  of  longi- 
tudinal fractures  near  the  middle  of  length  as  when  the  pipe 
is  burst  when  testing.  Such  failures  are  caused  by  expansion 
strains,  since  cylinders  are  twice  as  strong  circumferentially  as 
longitudinally  when  subjected  to  internal  pressures. 

The  simplest  method  is  to  provide  angles  in  the  line  of  piping, 
using  fittings  with  easy  turns,  and  have  the  legs  entering  the  elbows 
long  enough  to  take  up  the  expansion.  A  better  method,  especially 
for  high  pressures,  is  to  design  the  pipe  with  bends  of  long  radii, 
remembering  that  the  thicker  and  stiffer  the  material  the  longer 
should  be  the  radius.  Still  another  method  is  in  vogue  when  angles 
and  bands  cannot  be  used — that  is,  the  adoption  of  expansion-  or 


242  STEAM-BOILERS 

slip-joints.  Copper  pipes  seldom  require  slip-joints,  as  the  ma- 
terial, being  both  flexible  and  ductile,  can  usually  be  designed 
so  as  to  receive  the  required  bends.  Cast-iron,  wrought-iron 
and  steel  are,  however,  so  rigid  that  the  required  length  of  bend 
cannot  always  be  provided  and  slip-joints  must  be  made.  Some 
engineers  recommend,  out  of  preference,  such  straight  pipes  with 
slip-joints.  A  slip-joint  with  stuffing-box  is  illustrated  in  Fig.  94. 

These  joints  are  liable  to  give  trouble,  but  with  care  in  the 
design  of  the  whole  arrangement  they  need  not  be  more  trouble- 
some than  flanged  joints  subjected  to  cross-stresses  or  copper 
pipes  hardened  by  repeated  alteration  of  form. 

In  the  design  of  the  slip-joint  it  is  essential  that  the  lengthen- 
ing of  the  pipe  shall  actually  work  into  the  joint,  and  neither  enter 
so  far  as  to  bind  nor  pull  out  by  contraction  or  blow  out  by  pressure. 
This  is  accomplished  by  securely  fastening  some  part  of  the  pipe 
so  that  all  expansion  must  take  place  from  that  point,  and  by 
securing  the  stuffing-box  part  of  the  joint  in  a  fixed  position. 
When  both  the  joint  and  the  far  end  of  the  entering  pipe  be  fixed, 
there  is  no  danger  of  the  joint  blowing  out,  unless  there  be  a  bend 
in  the  pipe.  When  these  bends  occur,  safety-stays  should  be 
used  to  tie  the  bend  to  the  fixed  part.  These  safety-stays  are 
frequently  fitted  on  slip-joints  with  straight  pipes,  but  are  not 
necessary.  Safety-stays,  two  or  four,  according  to  circumstances, 
are  fastened  to  the  fixed  part  of  the  joint  and  pass  through  a  safety- 
flange  on  the  pipe,  located  about  18  inches  or  20  inches  back  from 
the  tail  pipe.  On  each  side  of  this  flange  there  is  a  nut  on  the  stay. 
When  the  pipe  is  cold  the  outside  nut  should  be  carefully  adjusted 
and  fixed  by  pinning,  so  that  it  cannot  be  carelessly  screwed  up 
against  the  flange  when  the  pipe  is  expanded  by  heat.  The  inside 
nut  prevents  the  pipe  from  pushing  too  far  into  the  stuffing-box,  and 
should  be  adjusted  in  like  manner  when  the  pipe  is  hot,  making  due 
allowance  for  movement  caused  by  vibrations  of  the  engine.  This 
inside  nut  may  be  omitted  altogether,  thus  preventing  any  thought- 
less tightening,  or  it  may  be  replaced  with  a  loose  ferrule  slipped 
over  the  stay  and  cut  the  proper  length  to  reach  between  the 
safety-flange  and  the  flange  on  the  joint. 

When  long  mains  are  used  to  carry  steam  at  low  or  moderate  pres- 
sures, the  expansion  can  be  provided  for  by  designing  a  double  offset 
with  six  elbows  secured  by  screw-threads.  With  this  arrangement 
the  amount  of  expansion  should  be  limited  by  adopting  frequent 


I 

2. 

2. 
5* 


P 

1. 


243 


244 


STEAM-BOILERS 


offsets  and  as  many  points  of  fixed  support,  since  the  expansion 
is  taken  up  by  the  working  of  the  threads.  Such  offsets  will  form 
a  pocket  for  water  which  must  be  drained  off  through  a  trap  of 
suitable  size. 

Flanges  are  used  to  join  the  pipe-lengths,  although  iron  or  steel 
pipes  when  less  than  three  inches  in  diameter  can  be  screwed 
together  with  couplings.  These  flanges  should  be  made  standard 
sizes,  so  as  to  be  interchangeable  and  insure  accurate  fitting. 

Flanges  for  copper  pipes  are  made  of  brass  or  of  composition, 
and  for  iron  or  steel  pipes  of  the  same  or  of  cast-iron,  cast-steel, 
malleable-iron,  or  wrought-iron  forged  into  shape  and  welded  on. 

Copper-pipe  flanges  are  brazed  on,  and  are  sometimes  riveted 
in  addition.  The  commonest  flange  is  illustrated  in  Fig.  95,  in 
which  the  flange  is  slightly  bevelled  so  as  to  admit  the  brazing 


i 


FIG.  95. — Plain  Flange  for  Copper  Pipe. 

solder.     It  is  the  simplest  arrangement  and  the  most  certain  that 
the  solder  will  be  where  most  needed.    Another  form,  Fig.  96,  has 


FIG.  96. — Collar  Flange  for  Copper  Pipe. 

a  collar  designed  to  give  additional  strength,  but  there  is  danger 
that  the  solder  will  not  enter  all  the  way,  as  shown  on  one 
side,  thus  becoming  firm  only  at  the  weak  end  of  the  collar. 
Another  form,  Fig.  97,  has  a  bevelled  sleeve  over  the  pipe  in  place 
of  the  collar,  but  then  there  is  danger  that  the  solder  will  not  run 
under  the  sleeve,  as  shown  on  one  side  of  the  figure.  It  is  best 
to  extend  the  pipe  through  the  flange  and  turn  the  edge  up  into 


BOILER  FITTINGS  245 

a  recess  in  the  flange-face.     The  flange  should  then  be  brazed  and 
riveted  on  as  in  Fig.  98. 

On  iron  and  steel  pipes,  when  less  than  16  inches  diameter,  the 


FIG.  97. — Plain  Flange  with  Sleeve  for  Copper  Pipe. 

flange  is  generally  screwed  on;  and  when  over  16  inches  diameter 
it  is  riveted  on.  The  objection  to  screwing  is  the  tendency  to  leak 
along  the  thread.  This  tendency  can  be  remedied  by  screwing 


FIG.  98. — Collar  Flange  with  Edge  of  Copper  Pipe  Turned  Over. 

the  flange  up  hard  on  the  pipe  (Fig.  99)  and  then  cutting  off  the 
projection  by  facing  up  both  the  flange  and  pipe  end;  or  by  leav- 


FIG.  99. — Flange  for  Iron  or  Steel  Pipe. 

ing  a  recess  in  the  collar  and  calking  in  lead,  as  shown  on  one  side 
of  Fig.  99.  Forged  flanges  welded  on  are  excellent,  but  cost  more 
than  screwed  flanges. 

The  faces  of  the  flanges  should  be  faced  true  so  as  to  fit  snug 
and  tight.  When  the  faces  are  plain,  a  gasket  of  rubber  or  other 
packing  material  is  used,  although  ground  flanges  may  be  bolted 


246 


STEAM-BOILERS 


metal  to  metal  and  made  tight.     Other  forms  of  face  are  used : — 
Fig.  100,  in  which  the  flanges  have  a  tongue  and  groove  turned 


FIG.  100.— Flanges  with  Tongue  and  Groove. 

on  the  faces  and  are  bolted  together  over  a  copper  ring  as  a  gasket. 
The  objection  is  sometimes  the  difficulty  of  removing  and  insert- 
ing a  pipe  section.  Fig.  101,  in  which  the  pipe  ends  are  flanged 


FIG.  101.—  Flanges  Cut  Away  to  Facilitate  Calking  Edges  of  Pipe. 

and  calked.  This  is  the  Walmanco  or  Van  Stone  joint,  and 
when  used  with  charcoal  iron  or  mild  steel  pipes  the  rivets 
are  omitted.  It  is  one  of  the  best  flanges,  as  it  is  simple 
and  can  be  kept  tight  under  heavy  pressures;  although  only 
the  best  grades  of  iron  or  steel  can  be  used,  as  poor  material 
will  not  stand  the  flanging.  Fig.  102,  in  which  the  faces  are 
made  with  a  recess  and  projection  to  fit  into  each  other.  This 
arrangement  prevents  the  gasket  from  being  blown  out,  no  matter 


BOILER  FITTINGS 


247 


what  the  pressure.  Fig.  103,  in  which  the  flanges  are  faced  and 
ground  true  and  bolted  directly  together,  an  arrangement  that  has 
proved  satisfactory  with  pressures  as  high  as  200  pounds. 

The   general  design   of  the  steam  -  piping  is   all  -  important. 
Short  and  direct  connections  between  boiler  and   engine,   with 


FIG.  102. — Flanges  with  Recess  and  Projection. 

Consideration  for  expansion  and  drainage,  are  to  be  preferred  as 
being  simple  and  offering  least  loss  from  condensation.  Design 
the  piping  so  that  there  will  be  no  pockets,  but  if  pockets  must 


FIG.  103.— Flanges  with  Faces  Ground  to  Fit. 

be  formed,  make  them  as  few  as  possible  and  of  ample  size  with 
drains.  It  is  an  easy  matter  for  steam  flowing  at  8000  feet  per 
minute  to  pick  up  water  and  carry  it  along. 

The  piping  should  always  pitch  for  drainage  in  the  direction  of 
the  current  of  steam,  and  horizontal  pipes  should  have  a  fall  of 


248  STEAM-BOILERS 

at  least  one  inch  in  every  ten  feet  run.  Horizontal  pipes  of  un- 
equal diameter  may  be  joined  by  an  eccentric  flange  on  the  smaller 
pipe,  so  that  the  bottom  of  the  pipes  on  the  inside  shall  be  level 
to  facilitate  drainage. 

The  area  of  the  steam-pipes  should  be  amply  large  for  their 
duty.  A  large  steam-pipe  is  a  good  fault,  especially  when  it 
supplies  engines  not  using  regular  quantities  of  steam,  as  it  then 
acts  as  a  reservoir.  With  very  high  pressures  or  with  a  regular 
flow  of  steam,  too  large  a  pipe  may  become  dangerous,  as  it  may 
serve  as  a  lodging-place  for  water. 

It  is  best  to  keep  as  much  of  the  piping  in  the  boiler-room  as  cir- 
cumstances will  permit  and  as  little  as  possible  in  the  engine- 
room,  because  less  damage  will,  as  a  general  thing,  be  caused  there 
in  case  of  an  accident,  and  the  chance  for  fatal  injury  to  the 
attendants  is  diminished. 

If  a  horizontal  distributing  steam-main  be  used,  the  feeder- 
pipes  from  the  boilers  should  each  rise  out  of  its  boiler  with  a  long 
bend  and  enter  the  top  of  the  main.  All  supply  branches  also 
should  take  off  from  the  top  of  the  main.  The  main  should 
be  drained  from  the  bottom  by  special  drain-pipes  and  the  feeders 
should  never  be  used  for  this  purpose,  as  water  will  not  flow  back 
against  the  velocity  of  the  steam. 

When  these  distributing  mains  are  short,  it  is  best  to  anchor 
them  in  the  middle  and  divide  the  expansion  between  the  ends. 
When  they  are  long,  place  an  expansion-joint  in  the  middle  and 
anchor  half  way  between  the  joint  and  the  ends. 

A  steam-main  frequently  has  its  area  diminished  as  branches 
are  taken  off,  and  is  terminated  in  a  bend  to  the  last  engine  or  in 
a  tee  with  two  branches  to  the  last  two  engines.  This  practice 
is  questionable  and  should  not  be  adopted  with  high  pressures. 
It  is  better  to  make  the  main  full  size  or  nearly  so  for  its  entire 
length  (unless  the  main  be  exceptionally  long),  giving  it  the  proper 
pitch,  say  one  inch  in  each  ten  feet  run,  and  to  terminate  it  in  an 
elbow,  turned  downward  with  a  vertical  pipe  attached  3  feet  or 
4  feet  long.  This  pipe  should  be  capped  and  a  drain  arranged 
discharging  into  a  trap,  a  receiving-tank,  or  back  to  the  boiler  if 
the  water  will  return  by  gravity. 

All  the  valves  on  the  steam-piping  should  be  so  located  as 
not  to  collect  water  when  either  closed  or  open.  When  the  pipe 


BOILER  FITTINGS  249 

rises  from  the  boiler  with  a  long  bend,  the  stop-valve  should  be  at 
the  top  of  the  bend  and  at  some  distance  from  the  boiler  connec- 
tion. It  is  best  to  have  two  valves  between  the  boiler  and  the 
distributing  main,  and  double  valves  are  sometimes  required  by 
local  ordinances. 

Globe  valves  should  not  be  used  on  horizontal  pipes,  as  they 
necessarily  form  a  pocket  for  water.  On  small  pipes,  an  offset 
globe  valve  may  sometimes  be  used,  but  in  all  cases  it  is  generally 
better  to  use  a  gate-valve  with  a  screw  movement.  If  the  pipe 
is  large,  it  is  well  to  provide  a  by-pass  in  connection  with  the 
gate-valve. 

A  gate-valve  should  always  be  placed  with  the  spindle  vertical, 
but  when  head  room  is  lacking,  the  valve  may  be  placed  hori- 
zontally. Gate-valves  never  should  be  set  with  the  spindle  point- 
ing downward,  as  then  the  valve  will  always  form  a  pocket,  no 
matter  what  the  opening  may  be,  and  the  gate  is  liable  to  be 
damaged  by  water-hammer  when  partly  open. 

A  stop-valve  placed  directly  on  the  boiler  nozzle  with  a  vertical 
pipe  leading  from  it  is  a  very  bad  arrangement,  as  water  is  sure 
to  collect.  If  such  an  arrangement  cannot  be  avoided,  place  a 
drain  on  the  upper  side  of  the  valve.  It  would  be  better  to  place 
an  angle  stop-valve  on  top  of  the  vertical  pipe  and  have  the  supply 
main  properly  pitched  away.  As  stop-valves  on  tops  of  boilers 
are  often  inconvenient  to  reach,  an  elbow  can  be  placed  on  the 
boiler  nozzle  and  the  pipe  led  from  it  with  the  valve  located  at 
some  accessible  point.  This  pipe  should  pitch  from  the  valve  in 
both  directions.  This  arrangement  is  very  good  when  head 
room  is  low. 

All  valves  should  be  located  for  easy  accessibility  in  order 
to  facilitate  rapid  control.  On  this  account  it  is  well  to  group 
them  as  near  together  as  may  be  convenient.  Usually  in  large 
stations  the  valves  can  be  so  placed  as  to  be  reached  from  a  light 
platform  or  gallery  suspended  from  the  roof  trusses. 

A  Stop-valve  should  be  placed  on  the  steam-pipe,  so  that  the 
steam  can  be  shut  off  at  any  time.  This  valve  should  be  close  to 
the  boiler,  and  is  frequently  mounted  on  a  nozzle  attached  to  the 
boiler  shell,  although  its  best  location  must  depend  on  the  piping 
design.  The  valve  should  be  operated  by  a  screw,  and  when  of 
the  globe  pattern  be  arranged  to  close  down  against  the  pressure, 


250  STEAM-BOILERS 

that  it  may  be  repacked  around  the  spindle  when  required.  It 
never  should  be  a  quick-opening  valve  of  the  gate  or  lever  type. 

Stop-valves  are  generally  made  of  cast-iron,  with  the  valve, 
seat  and  spindle  of  gun-metal  or  bronze.  The  best  valves  are 
made  all  of  bronze,  but  this  is  a  refinement  little  adopted  except 
in  naval  vessels.  In  very  important  work,  and  in  some  war 
vessels,  the  stop-valve  is  made  to  close  automatically,  whenever 
the  pressure  in  the  boiler  falls  below  that  in  the  steam-main, 
and  to  automatically  open  again  when  the -requisite  pressure  has 
been  regained.  This  is  done  to  prevent  total  shut-down  in  cases 
of  damage  to  one  boiler,  when  a  battery  of  boilers  are  feeding 
into  a  common  main. 

Since  bronze  and  cast-iron  have  different  coefficients  of  ex- 
pansion, stop-valves  often  leak  at  the  seat  unless  the  seats  be 
well  secured  into  the  cast-iron.  If  the  valve  be  fitted  with  wings 
to  guide  its  motion,  these  wings  should  be  curved  slightly,  so  as 
not  to  bind  against  the  seat  except  when  the  valve  is  down. 

The  area  through  the  stop-valve  should  exceed  that  of  the 
steam-pipe,  so  as  not  to  cause  loss  of  pressure  due  to  friction. 

In  all  globe  and  angle  valves  the  full  pressure  is  on  the  valve 
when  closed,  and  the  load  is  carried  by  the  yoke  or  bridge  and 
by  the  spindle.  These  parts,  therefore,  should  be  amply  strong. 
The  rule  for  size  of  spindle  in  Seaton's  Manual  of  Marine  En- 
gineering is: 

dia.  of  valve, ,    / 

Dia.  of  spindle  =  -  — =7r-  —  X  V  pressure  +  J-  inch. 
oU 

It  is  well  to  have  the  yoke  so  designed  that  it  will  carry  a  spindle 
for  regrinding  the  seat  when  necessary. 

The  drips  from  all  steam-mains  should  lead  to  a  receiving- 
tank,  and  the  water  be  automatically  pumped  back  to  the  boiler. 
If  the  drips  lead  from  mains  under  different  pressures,  then  the 
drips  should  be  trapped.  Sometimes  the  drips  can  be  drained 
back  by  gravity  into  the  boilers  through  a  check-valve  at  the 
boiler,  but  the  receiving-tank  system  is  generally  the  better. 

All  condensed  steam  containing  grease  or  oil  should  be  kept 
separate  and  passed  through  a  grease  extractor  or  be  filtered 
before  being  returned  to  the  boilers. 

The   Dry-pipe,  sometimes   called  the  "internal  pipe,"   is    an 


BOILER  FITTINGS  251 

arrangement  for  drawing  steam  from  all  parts  of  the  steam  space, 
and  is  a  very  good  device  for  obtaining  dry  steam  and  for  pre- 
venting priming.  It  consists  of  a  pipe  fitted  inside  of  the  boiler 
and  connected  to  the  steam-main  (Figs.  11,  16,  17,  18,  19  and  20). 
This  pipe  is  perforated  with  holes  or  slots  on  its  upper  side  only, 
the  ends  being  closed.  There  should  be  |-inch  or  f-inch  holes  in 
the  bottom  near  the  ends  to  act  as  drains.  The  aggregate  area 
of  the  holes  for  steam  entrance  into  the  dry-pipe  should  be  about 
equal  to  that  of  the  steam-main. 

The  dry-pipe  is  frequently  made  as  a  trough  or  half  pipe,  the 
top  of  the  boiler  shell  forming  the  cover  (Figs.  12,  26  and  27). 
The  edges  of  the  trough  are  kept  about  one-half  inch  from  the 
shell,  so  as  to  form  a  passage  for  the  steam. 

The  dry-pipe  operates  by  drawing  steam  from  the  length  of 
the  steam  space,  and  therefore  renders  the  separation  of  the 
steam  from  the  water  more  uniform  and  prevents  local  differences 
in  pressure,  which  cause  uneven  ebullition  and  priming. 

Dry-pipes  may  be  made  of  cast-iron,  which  is  the  cheapest 
material  and  obviates  any  chance  of  galvanic  action;  or  of 
wrought-iron  or  steel,  which  are  both  light  and  serviceable;  or 
of  brass  or  copper,  which  are  the  most  expensive  and  most  easily 
worked,  but  objected  to  by  engineers  as  tending  toward  gal- 
vanic action.  Copper  pipes  should  be  tinned. 

The  dry-pipes  are  held  in  place  by  lugs  or  bands  bolted  to 
the  shell. 

Boiler-feed.  Every  boiler  should  have  two  independent 
means  of  feeding  in  the  water,  and  marine  boilers  subject  to  in- 
spection are  required  to  be  so  fitted.  Many  stationary  boilers, 
however,  have  only  one  feeding  attachment. 

Each  feed-pipe  entering  the  boiler  should  have  its  own  back- 
pressure or  check-valve,  so  situated  that  the  check  will  fall  by 
gravity  into  the  closed  position,  and  it  should  be  placed  as  near 
the  boiler  as  possible,  with  a  good  screw-closing  stop-valve  be- 
tween it  and  the  boiler.  This  latter  valve  is  used  for  shutting  off 
the  connections  to  affect  repairs  to  the  check-valve  or  piping. 

The  feed-pipes  should  be  of  copper  or  brass,  as  those  metals  are 
the  most  durable  and  present  the  neatest  appearance.  All  valves 
on  the  feed-pipes  may  be  of  the  globe  pattern,  but  good  gate- 
valves  are  better,  except  for  the  stop-valve,  as  they  offer  less 


252  STEAM-BOILERS 

frictional  resistance  and  make  a  more  direct  passage  for  the 
water.  For  similar  reasons  all  elbows  and  bends  should  be  of 
the  long  radius  type. 

If  any  of  the  feed-water  comes  from  condensed  steam  con- 
taining oil  or  grease,  it  should  be  filtered,  as  also  any  water  that 
is  muddy  or  carries  sediment  in  suspension. 

There  is  some  diversity  of  opinion  as  to  the  best  place  to  admit 
the  feed.  When  the  feed  is  very  hot,  there  can  be  less  difference 
in  actual  evaporation,  no  matter  at  what  point  it  enters.  Un- 
fortunately the  feed-water  is  often  cold,  or  rather  much  colder 
than  the  water  in  the  boiler,  and  then  it  would  appear  best  to  so 
admit  it  that  it  will  assist  the  natural  circulation  and  at  a  place 
where  it  will  never  strike  directly  against  hot  heating  surfaces, 
even  when  the  feed  intended  for  a  battery  of  boilers  be  concen- 
trated into  one  by  accident  or  otherwise. 

The  best  place  can  only  be  determined  after  careful  study  of 
the  type  of  boiler  and  of  the  scale-making  qualities  of  the  water. 
Many  prefer  to  have  it  enter  near  the  bottom,  some  at  the  coldest 
part,  while  others  favor  its  admission  near  the  water-line  and  at 
some  place  where  there  is  a  natural  downward  current. 

The  consensus  of  opinion  is  to  admit  the  feed  near  the  water- 
line,  and  to  distribute  the  discharge  through  a  number  of  small 
openings,  so  as  to  prevent  a  solid  jet  of  more  or  less  force  from 
entering.  If  the  pipe  enters  near  the  water-line  and  turns  down 
on  the  inside,  care  must  be  taken  that  the  open  end  should  be 
always  in  the  steam  space  or  below  the  lowest  water-line,  and 
never  be  covered  and  exposed  alternately  by  possible  variations 
in  the  water-level.  If  the  feed-pipe  fills  with  steam,  loud  explosive 
noises  will  result  as  condensation  takes  place.  These  explosions, 
while  not  dangerous,  are  extremely  unpleasant  and  are  apt  to 
cause  injury  and  leaks  in  the  joints.  Such  action  sometimes 
occurs  in  improperly  piped  marine  boilers,  which  are  subject  to 
wide  variation  of  water-level  on  account  of  the  rolling  and  pitching 
of  the  ship. 

A  very  good  plan  is  to  carry  the  pipe  into  the  steam  space, 
and  to  terminate  it  in  a  horizontal  branch,  just  above  the  water- 
line,  with  holes  so  that  the  feed  will  enter  as  spray.  When  the 
steam  space  is  contracted,  it  would  be  better  to  place  the  dis- 
tributing pipe  just  below  the  water-line.  If  the  water  carries 


BOILER  FITTINGS 


253 


much  lime  or  magnesia,  it  would  be  better  to  shorten  the  internal 
arrangement,  leave  the  ends  of  the  pipe  open  and  omit  the  holes. 

Another  good  plan,  especially  with  bad  water,  is  to  let  the  feed 
enter  an  open  trough  carried  inside  the  boiler  just  above  the  water- 
line.  As  the  trough  fills,  the  water  will  spill  over  the  sides.  In 
place  of  the  trough,  a  disk  or  inverted  cone  may  be  used.  This 
trough  or  cone  will  distribute  the  feed,  heat  it  and  retain  con- 
siderable deposit  which  can  be  removed  without  injury  to  the  boiler. 

The  disadvantage  of  any  internal  piping  is  the  danger  of  de- 
rangement due  to  scale  formation  within  and  the  consequent 
closing  of  the  pipe.  The  advantage  is  that  the  feed  has  a  chance 


o    o    o    o    o 

o     o     o     o 


ri 


O      O      O      O      O 
oooo 


FIG.  104. — Feed-pipe  Entrance  with  Distributing  End. 

to  become  heated  before  it  enters  the  boiler.  An  important 
advantage  in  having  the  feed-pipe  enter  near  the  water-line  is  that 
the  water  in  the  boiler  cannot  be  blown  out  should  the  check-valve 
fail  to  work  from  any  cause. 

No  matter  where  the  feed  enters,  it  should  be  fed  in  continu- 
ously and  in  just  sufficien  quantity  to  equalize  the  water  evapo- 
rated, thus  maintaining  a  constant  water-level.  The  practice  of 
intermittent  feed — that  is,  permitting  the  water  to  fall  a  certain 
amount  before  refilling — is  objectionable  and  uneconomical. 

Figs.  11,  12,  15,  17,  18,  104,  105  and  106  show  various  ways  in 
common  use  for  feed-pipes  entering  boilers. 


254 


STEAM-BOILERS 


The  feed-water  should  be  as  hot  as  possible,  both  for  the  sake 
of  economy  and  for  preventing  local  contraction  stresses  caused  by 


FIG.  105. — Feed-pipe  Entrance. 

the  feed  striking  hot  surfaces.     It  is  forced  into  the  boiler  by 
injectors  or  pumps.     Many  boilers  have  two  injectors,  others  two 


TROUGH 


FIG.  106. — Feed-pipe  Entrance. 

pumps,  and  some  one  injector  and  one  pump,  so  as  to  provide 
duplicate  systems. 

Injectors  or  Inspirators  are  manufactured   in  standard   sizes 
and  merely  have  to  be  piped  or  connected  (Fig.  107). 


BOILER  FITTINGS 


255 


Injectors  are  seldom  arranged  to  feed  more  than  one  boiler. 
They  are  capable  of  lifting  the  supply  water  to  a  height  of  about 
25  feet,  the  height  depending  upon  the  steam  pressure;  but  with 
a  high  lift  their  action  is  not  always  reliable.  For  ordinary  con- 
ditions, the  lift  should  not  exceed  five  or  six  feet. 

The  supply  may  be  under  pressure,  but  it  will  be  found  much 
better  to  use  a  tank  with  a  supply  pipe  fitted  with  a  "ball  cock," 
and  arrange  the  injector  to  lift  the  water  from  it. 


A  Coupling  Nut 
B    Tail  Pipe 
X    Overflow  Cap 
E    Nut  for  Stem  M 


S     Steam  Jet  _ 

V    Suction  Jet 

C-D-R   Combining  and  Delivery  Tube 

and  Auxiliary  Check 
P    Overflow  Valve 
O    Steam  Plug 
M    Steam  Valve  and  Stem 
N    Packing  Nut 
K    Steam  Valve  Handle 


FIG.  107. — The  Metropolitan  Injector. 

The  steam-pipe  connection  should  lead  from  the  steam  space 
of  the  boiler,  so  as  not  to  be  shut  off  by  the  main  stop-valve.  This 
pipe  should  have  a  valve  near  the  injector  to  control  the  steam- 
supply  ;  and  it  is  best  to  place  another  valve  near  the  boiler,  which 
can  be  closed  in  case  of  accident  to  the  piping.  The  other  connec- 
tions are  to  the  water-supply,  the  boiler-feed  and  the  overflow,  all 
of  which  should  be  as  direct  as  possible. 

The  principle  upon  which  these  ingenious  devices  operate  is  as 
follows:  Steam  under  pressure  flows  through  a  free  opening  at 
a  greater  velocity  than  water  under  the  same  pressure.  When 
the  steam  is  turned  on,  it  issues  through  a  nozzle,  sucks  up  the 
supply  water,  condenses  and  discharges  through  the  overflow. 
The  impact  of  the  steam  on  the  water  gives  to  the  latter  much  of 


256  STEAM-BOILERS 

its  velocity.  The  momentum  of  this  water  is  sufficient  to  raise 
the  check-valve  and  enter  the  boiler  against  the  steam  pressure,  as 
soon  as  the  overflow  has  been  closed.  Sometimes  the  steam  will 
blow  back  through  the  suction  or  water-supply  pipe,  rather  than 
enter  the  boiler,  a  condition  generally  made  apparent  by  the  noise. 
When  such  action  occurs,  the  injector  must  be  shut  down  by  clos- 
ing off  the  steam  and  started  afresh. 

Injectors  may  be  operated  with  exhaust  steam  from  an  engine 
if  at  sufficient  pressure,  but  then  the  steam  passages  must  be 
correspondingly  larger. 

The  injector  is  really  a  heat-engine  without  moving  parts, 
the  energy  stored  in  the  steam  being  converted  into  work  by  plac- 
ing a  column  of  water  into  motion,  and  by  overcoming  the  frictional 
resistances.  In  order  to  accommodate  itself  to  variations  in 
pressure  of  steam  and  temperature  of  feed  and  supply  water,  the 
apparatus  is  so  made  as  to  adjust  the  openings  for  steam  and  water. 

The  injector  has  the  virtue  of  heating  the  feed,  but  if  the  water- 
supply  be  so  hot  as  not  to  condense  the  steam,  it  will  not  operate 
against  the  boiler  pressure. 

As  a  pumping  apparatus,  an  injector  is  very  inefficient;  but  as 
a  boiler-feeder,  its  efficiency  is  high,  since  the  heat  of  the  steam, 
except  the  small  amount  lost  by  radiation,  re-enters  the  boiler. 

Feed-pumps  are  purchased  from  the  makers  in  standard  sizes 
to  suit.  They  are  nearly  always  made  double-acting,  but  may  be 
single  or  duplex,  horizontal  or  vertical.  Duplex  pumps  are  more 
reliable  than  single  pumps,  as  they  are  not  so  apt  to  catch  and  stop, 
but  are  more  expensive.  Vertical  pumps  are,  in  general,  better 
than  horizontal  ones,  although  for  ordinary  boiler-feeding  pur- 
poses, there  is  little  choice.  For  marine  work  the  vertical  pump 
is  much  in  favor,  as  it  can  be  easily  fastened  to  a  bulkhead  and 
thus  be  kept  off  the  floor. 

Feed-pumps  should  always  have  a  capacity  in  excess  of  the 
ordinary  or  average  requirement.  One  pump  may  feed  a  battery 
of  boilers,  and  when  so  arranged  the  water  is  pumped  into  a  supply 
main  extending  along  the  fronts  of  the  boilers,  from  which  branches 
are  led  to  each  boiler.  The  supply  to  each  is  controlled  by  a 
valve  on  the  branch  pipe. 

The  steam-pipe  to  the  pump  should  lead  directly  from  the 
boiler,  so  as  to  be  operative  at  times  when  the  main  stop-valve 


BOILER  FITTINGS  257 

is  closed.  When  the  supply  water  is  hot  the  pump  should  fill  by 
gravity  and  not  by  suction,  as  in  the  latter  case  the  hot  water  is 
liable  to  vaporize  under  the  vacuum  and  the  pump  may  fail  to  lift 
the  water. 

When  the  engine-room  is  separate  from  the  boiler-room,  it 
is  sometimes  a  question  whether  the  feed-pump  should  be  in  the 
engine-room  directly  under  the  control  of  the  engineer,  or  be  in 
the  fire-room  and  exposed  to  the  dirt  and  dust.  Other  things 
being  equal,  it  is  best  to  place  it  in  the  boiler-room  under  the 
management  of  the  boiler  attendant,  and  only  retain  an  attendant 
who  is  trustworthy  and  competent  to  maintain  a  proper  water- 
level. 

The  feed-pump  may  be  connected  to  and  driven  by  the  main 
engine,  a  practice  which  is  common  in  marine  work  and  with 
engines  that  operate  continuously  for  long  periods  at  compara- 
tively steady  power.  It  is  more  economical  to  operate  a  feed-pump 
by  the  main  engine,  as  the  consumption  of  steam  per  horse-power 
is  much  less  in  the  main  engine  than  in  any  form  of  independent 
pump.  This  practice,  however,  is  not  general,  because  the  in- 
dependent pump  is  always  available  for  use  or  repair,  whether  the 
main  engine  is  running  or  stopped. 

Feed-water  Heaters.  The  feed-water  should  always  be  as 
hot  as  possible,  since  less  heat  will  be  required  to  evaporate  it, 
and  since  there  is  less  danger  of  injury  from  local  contraction 
caused  by  impact  of  cold  water.  A  good  feed-water  heater  is  a 
very  desirable  adjunct  to  a  boiler  plant. 

The  saving  effected  by  a  hot  feed  is  considerable,  and  when 
this  can  be  accomplished  at  a  cost  (including  interest,  deprecia- 
tion, maintenance  and  repairs)  low  enough  to  establish  a  net  sav- 
ing, a  heater  should  always  be  installed.  The  gross  saving  in 
heat-units  can  be  computed  with  the  aid  of  a  steam-table,  or  from 
the  formula  for  the  total  heat  of  evaporation  (see  Chapter  I).  The 
tables  that  are  usually  published  showing  the  saving  effected,  give 
the  gross  saving  and  do  not  consider  the  items  of  cost  mentioned 
above. 

The  water  may  be  heated  in  various  ways.  The  exhaust  steam 
may  be  condensed  in  a  surface  condenser  and  be  pumped  back  to 
the  boiler.  The  water  may  be  made  to  pass  through  a  heater,  which 
can  be  warmed  by  exhaust  steam,  by  live  steam  taken  direct  from 


258  STEAM-BOILERS 

the  boiler  or  by  the  hot  gases  in  the  stack.  Circumstances  must 
determine  the  proper  method  to  adopt.  Live  steam  will  cost 
more  to  produce  than  the  saving  in  the  heater,  on  account  of  loss 
from  radiation,  but  it  may  pay  through  prolonged  life  of  the 
boiler  and  the  lessened  cost  of  removing  scale. 

The  surface  condenser  is  a  vessel  into  which  the  exhaust  steam 
enters  and  is  condensed  by  air  or  water,  the  condensed  steam  being 
made  available  for  boiler-feeding.  As  the  condensed  steam  con- 
tains the  cylinder  oil  carried  over  from  the  engine,  it  should  be 
filtered  before  being  returned  to  the  boiler.  Surface  condensers  are 
used  in  marine  work,  as  they  save  the  fresh  water,  and  are  suitable 
for  stationary  practice  when  water  is  expensive  or  of  bad  quality. 
Air  is  seldom  used  as  a  cooling  medium,  due  to  its  high  specific 
heat.  When  water  for  circulating  or  cooling  purposes  is  scarce  or 
expensive,  cooling  towers  or  shallow  tanks  can  be  used,  in  which 
the  same  water  is  cooled  by  air,  so  that  it  can  be  made  available 
again  for  condensing  purposes. 

Heaters  may  be  of  the  "open"  or  " closed"  type.  In  the 
former  the  feed-water  is  sucked  through  the  heater  and  pumped 
hot  into  the  boiler ;  while  in  the  latter  the  water  is  pumped  through 
the  heater  under  boiler  pressure.  A  heater  should  be  easy  to 
clean,  and  be  arranged  with  a  by-pass  so  that  it  can  be  cut  out  of 
the  system  for  cleaning  or  repairs. 

The  ordinary  closed  heater  of  the  Goubert  type  (Fig.  108)  con- 
sists of  a  shell  containing  straight  tubes.  The  feed  passes  through 
these  tubes  and  is  heated  by  the  exhaust  (or  live)  steam  that  is 
allowed  to  enter  the  shell.  The  usual  form  of  connection  has  the 
steam  entrance  near  the  bottom,  and  in  such  cases  air  sometimes 
will  collect  in  the  upper  part  of  the  shell  and  be  difficult  to  re- 
move even  if  an  automatic  air  relief  valve  be  fitted.  A  better  plan 
is  to  let  the  steam  enter  near  the  top  and  be  drawn  off  as  usual  at 
the  bottom,  with  the  double  connection  joined  by  a  by-pass  pipe 
and  valves.  This  method,  however,  is  more  expensive.  This 
class  of  heater  should  not  be  used  with  waters  containing  large 
quantities  of  the  salts  of  lime  and  magnesia.  The  Berryman 
heater  contains  U-shaped  tubes  through  which  the  steam  cir- 
culates. 

With  all  scale-forming  waters,  heaters  of  the  type  of  the  Hoppes 
Combined  Feed- water  Heater  and  Purifier  (Fig.  109)  are  excellent. 


BOILER   FITTINGS 


259 


This  heater  consists  of  a 
cylindrical  shell  containing 
trays,  one  above  the  other. 
The  feed  enters  at  the  top 
and  drips  from  tray  to  tray, 
depositing  its  scale  in  the 
process,  and  at  the  same  time 
is  heated  by  steam  under 
boiler  pressure.  The  trays 
can  be  removed  and  the  scale 
cleaned  off. 

Open  heaters  of  the  Coch- 
ran  type  (Fig.  110)  consist  of 
a  vessel  through  which  the 
feed  falls  as  spray,  and  is 
warmed  by  exhaust  (or  live) 
steam.  The  heater  is  in 
reality  closed  by  a  back-pres- 
sure valve,  so  set  as  not  to 
maintain  an  excessive  back 
pressure  on  the  engine  and 
to  relieve  the  surplus  of 
steam.  When  improperly 
made  or  set,  open  heaters 
may  flood  and  choke  the  ex- 
haust, and  therefore  should 
be  fitted  with  an  automatic 
control  valve  to  regulate  the 
cold-water  supply.  Open 
heaters  are  easier  to  clean 
than  closed  heaters,  but  as 
the  feed  comes  in  contact 
with  the  steam,  they  should 
be  equipped  with  a  grease 
and  oil  extractor. 

A  heater  may  be  placed 
in  the  smoke-flue,  and  be 
warmed  by  the  escaping  gases 
of  combustion.  Such  an  ar- 


FIG.  108. — The  Goubert  Feed-water 
Heater— Closed  Type. 


260  STEAM-BOILERS 

rangement  is  usually  called  an  " Economizer."  The  "Green"  type 
of  economizer  is  the  most  common,  consisting  of  a  set  of  cast-iron 
pipes  about  4  inches  in  diameter  and  8  or  10  feet  long,  surrounded 
by  scrapers  to  keep  the  external  surfaces  free  from  soot  (Fig. 
111).  These  scrapers  are  worked  by  chains  from  the  outside  of 
the  flue.  This  class  of  heater  should  be  made  accessible,  and  this 
can  best  be  accomplished  by  dampers  and  a  by-pass  flue. 

Such  heaters  must  be  made  amply  strong,  as  steam  is  liable 
to  form  in  them.  Being  placed  in  the  flue,  they  offer  a  resistance 
to  the  draft  and  cool  the  gases,  so  that  they  operate  most  advan- 
tageously when  the  draft  is  sufficiently  strong.  The  reduced  tem- 
perature of  chimney  gases  and  the  resistance  or  friction  to  their 
passage  diminish  the  intensity  of  the  draft.  Their  economy  lies  in 
the  fact  that  they  recover  some  of  the  heat  passing  up  the  stack. 

There  is  a  question  with  natural-draft  plants,  whether  it  would 
not  be  better  to  have  the  heater  surface  in  the  boiler  itself  by 
having  a  high  ratio  of  heating  surface  to  grate  surface  and  thus  re- 
ducing the  temperature  of  the  escaping  gases  to  a  minimum.* 

The  first  cost  of  an  economizer  is  about  equal  to  that  for  the 
same  amount  of  heating  surface,  but  economizer  surface  costs 
less  to  keep  in  repair  and  no  more  to  keep  clean  than  boiler  heating 
surface  of  equal  area.  In  general,  all  plants  would  be  benefited 
by  an  economizer  when  properly  designed,  except  very  small 
plants,  or  those  in  which  simplicity  is  of  more  impo  tance  than 
economy,  or  those  in  which  the  boiler  power  is  ample  and  the 
gases  escape  at  very  low  temperatures.  Economizers  have  an 
advantage  in  the  reserve  of  a  large  body  of  hot  water  for  use  in  a 
sudden  call  for  steam. 

For  the  improvement  of  uneconomical  plants  or  for  reducing  the 
wear  due  to  cold  feed,  they  are  highly  efficient;  but  with  waters 
of  bad  scaling  properties,  heating-coils  in  the  flue  are  troublesome. 
For  such  hard  waters,  some  form  of  closed  heater  designed  to 
take  care  of  the  scale,  like  the  Hoppes,  is  better. 

The  tube  surface  of  a  heater  of  the  Berryman  type  is  generally 
taken  from  J-  to  ^-square  foot  for  each  boiler  horse-power,  while  that 
of  an  economizer  is  usually  from  J  to  ^  of  the  heating  surface  of  the 
boiler. 

*  This  minimum  must  be,  however,  higher  than  that  of  the  steam  in  the 
boiler,  in  order  to  obtain  any  effect  from  the  last  heating  surface. 


BOILER   FITTINGS 


261 


262 


STEAM-BOILERS 


EXHAUST 


INLET 


WATER  SUPPLY 


FIG.  110. — Cochran  Feed-water  Heater — Open  Type. 


BOILER  FITTINGS 


263 


264 


STEAM-BOILERS 


Filters  are  arranged  in  many  different  ways,  according  to  the 
specific  object  desired.  When  sediment  or  sand  is  to  be  removed 
some  good  form  of  sand,  gravel  or  charcoal  filter-bed  is  generally 
to  be  preferred,  but  must  be  arranged  for  easy  cleaning. 

Closed  feed-water  heaters  designed  to  catch  the  deposit  or  scale 
formation  act  in  a  sense  as  filters  or  purifiers. 


TJ cr 


© 


(0) 


o  J 


SUCTION 
TO  PUMP 


FIG.  112. — Hot-well  Filter-box. 


When  oil  or  grease  is  to  be  removed,  as  in  the  filtration  of  con- 
densed steam  from  a  surface  condenser,  the  simplest  form  is  to 
allow  the  discharge  from  the  air-pump  to  pass  into  a  hot  well  or 
box  divided  by  partitions.  In  these  compartments  is  placed  some 
filtering  substance,  as  sponges,  hay,  salt  meadow  grass,  excelsior 
(wood  fibre),  etc.  The  filtered  water  or  suction  to  the  boiler  feed- 
pump is  taken  from  the  last  compartment  (see  Fig.  112).  The 
filtering  material  is  removed  for  cleaning  and  may  be  used  again. 

The  water  may  be  filtered  by  being  passed  through   canton- 


BOILER  FITTINGS 


265 


flannel  or  some  similar  substance,  which  can  be  arranged  so  as  to 
be  renewed.  The  simplest  of  these  filters  are  of  the  Edmiston 
type,  and  consist  of  a  perforated  cylin- 
der over  which  the  canton-flannel  bag  is 
stretched.  The  apparatus  is  enclosed 
and  connected  on  the  feed-pipe  between 
the  feed-pump  and  the  boiler  check- 
valve.  There  should  be  a  by-pass,  to 
use  when  the  filter  is  being  cleaned 
(Figs.  113  and  114). 

Mud-drums  consist  of  a  closed  cylin- 
drical shell  attached  to  the  lowest  part 
of  a  boiler  and  into  which  the  feed- water 
is  pumped.  The  mud,  sediment,  etc., 
in  the  feed-water  is  supposed  to  settle 
in  the  drum  before  the  feed  passes  into 
the  boiler  proper  (Fig.  115).  They  are 
not  in  universal  use  as  their  efficiency  is 
doubtful,  except  with  water  containing 
a  heavy  sediment  in  mechanical  sus- 
pension and  with  boilers  in  which  the 
convection  currents  are  not  very  rapid. 

Owing  to  the  deposit  in  the  mud- 
drums,  they  should  not  be  placed  so  as 
to  receive  the  direct  heat  of  the  fire. 
This  precaution  is  not  always  taken  and 
then  the  drums  are  liable  to  burn  and 
may  be  a  source  of  danger.  The  drums 
are  made  of  cast-iron  or  steel,  and  inci- 
dentally they  act  as  feed-water  heaters. 

Water-tubular  boilers  are  frequently 
fitted  with  mud-drums  which  are 
worked  in  as  part  of  the  design. 

With  bad  waters  it  would  be  pref- 


o 


STRAINER  PLATES 


OoOOOOOOO  OOOOOO 
OOOO  OOOOOOOQOOOO 

ooooooooooooooo 
oooooooooooooooo 

oooooo  ooooooooo 
oooooooooooooooo 


OOO  O  OCO  O  OOO  O  OOOO 

ooooooooooooooo 

OOOO     OOOO     OOOO     OOOO 

ooooooooooooooo 

OOOO   OOO  OOOOOOOOO 
OOO  OOOOOOOOOOOO 


FIG.  112a. — Details  of 

Fig.  112. 

erable  to  use  some  suitable  form  of  filter  rather  than  any  form  of 
mud-drum. 

Blow-offs.  Every  boiler  must  have  a  blow-off  to  discharge 
the  water.  There  should  be  two  blow-offs  in  all  important  boilers, 
one  known  as  the  "  bottom  blow"  and  the  other  as  the  "  surf  ace 


266 


STEAM-BOILERS 


blow."     The  function  of  the  latter  is  to  remove  the  scum,  grease 
and  light  particles  of  dirt  or  precipitate  that  float  or  are  carried 


T^ BOILER  Q 


//FEED  WATER 


FIG.  113. — Edmiston  Type  of  Feed-water  Filter. 


FIG.  114. — Rankine's  Patent  Feed-water  Filter. 

in  suspension  by  the  convection  currents;  and  of  the  former,  to 
remove  the  mud,  sludge  and  heavy  sediment  that  settles  to  the 
bottom. 


BOILER  FITTINGS 


267 


The  surface  blow-off  pipe  is  usually  made  bell-mouthed,  with 
the  end  placed  at  the  working  water-level.  The  opening  of  the 
bell  should  face  a  surface  current,  that  the  water  may  have  a  nat- 
ural tendency  to  flow  into  the  -pipe.  There  should  be  a  good 
valve  on  the  discharge  pipe  as  near  the  boiler  as  possible. 

The  bottom  blow-off  pipe  should  enter  at  or  near  the  bottom 
of  the  boiler.  If  it  is  not  convenient  to  have  it  enter  through  the 
bottom,  then  an  internal  pipe  should  be  fitted  and  carried  down 
to  the  desired  point.  This  internal  'pipe  may  be  of  iron  or  copper, 


FIG.  115. — Mud-drum. 

although  copper  may  induce  galvanic  action  unless  tinned.  When 
used  to  discharge  mud  or  sludge,  the  internal  pipe  may  be  extended 
along  the  bottom  and  be  perforated  so  as  to  draw  from  all  parts; 
but  if  the  water  is  of  the  bad  scaling  kind,  such  a  pipe  will  be  liable 
to  become  choked.  On  the  discharge,  there  should  be  a  valve 
placed  as  near  the  boiler  as  possible.  This  valve  should  be  of  the 
straight-way,  taper-plug  pattern,  as  such  cocks  can  be  plainly 
seen  to  be  open  or  shut,  and  only  carelessness  will  leave  them 
partly  open.  A  screw- valve -might  have  a  chip  of  scale  under  it, 
although  the  attendant  may  think  it  closed.  A  good  type  of  valve 
is  of  the  plug  variety,  with  a  gland  around  the  stem  and  asbestos- 
packed.  Taper-plug  cocks  are  apt  to  corrode  and  stick.  This  can 
be  overcome  by  daily  use  and  by  making  them  of  composition. 
A  taper  of  1  in  6  is  found  satisfactory,  and  to  prevent  uneven 
wear  they  can  be  made  to  make  a  complete  turn. 

The  discharge  from  the  bottom  blow  always  should  be  made 


268 


STEAM-BOILERS 


a  sight  discharge,  so  that  failure  to  close  the  valve  will  be  at  once 
apparent.  An  invisible  discharge  is  always  attended  with  danger, 
since  the  water  might  all  leave  the  boiler  and  not  be  noticed  until 
too  late.  Furthermore,  the  blow-off  discharges  should  be  inde- 
pendent from  each  boiler  and  not  be  connected  together. 

The  bottom  blow-off  pipes  are  often  exposed  to  the  action  of 
the  hot  gases,  and,  as  they  may  fill  with  scale  and  have  no  cir- 
culation in  them,  they  are  then  liable  to  burn.  They  should  be 
protected  from  the  hot  gases  by  placing  lengths  of  pipe  (cast-iron 
or  tile  *)  around  them.  Never  set  them  in  brickwork  where  they 
cannot  be  inspected  and  where  dampness  may  corrode  them  un- 
noticed. By  connecting  a  circulating-pipe  on  the  boiler  side  of 
the  valve,  a  constant  circulation  of  water  may  be  maintained> 
with  good  result  as  regards  overheating  and  durability. 

The  surface  blow-off  is  generally  made  from  1  inch  to  2  inches 
in  diameter,  and  the  bottom  blow-off  from  1^  inches  to  3  inches, 
according  to  circumstances. 


FIG.  116. — Surface  Blow-off. 

Boilers  should  never  be  blown  off  at  pressures  exceeding  four 
or  five  pounds  of  steam,  as  serious  injury  can  be  caused  by  sudden 
cooling.  Repeated  short  blows  at  frequent  intervals,  however, 
are  recommended. 

When  boilers  are  located  in  cities,  the  discharge  should  enter 
a  cooling-tank  before  it  passes  to  the  sewer,  but  this  tank  or  sump 
should  be  arranged  so  that  a  pressure  cannot  be  maintained  in  it 
under  any  possibility.  Serious  accidents  have  been  reported 
from  this  neglect. 

A  surface  blow  is  illustrated  in  Fig.  116,  and  bottom  blows  in 
Figs.  10,  11  and  12. 

*  Fire-clay  tile  having  alternate  ends  made  to  fit  with  a  recess  and  pro- 
jection. See  Fig.  12. 


BOILER  FITTINGS 


269 


Safety-valve.  Every  boiler  should  have  a  safety-valve,  and 
when  the  required  size  of  the  valve  is  large,  it  is  best  to  use  two 
or  even  three  smaller  ones  having  an  equivalent  area.  Safety- 
valves  are  liable  to  stick  fast  on  their  seats,  and  should  be  raised 
by  hand  at  least  once  every  day.  Safety-valves  should  be  simple 
and  of  a  type  not  easily  deranged. 

Internally  weighted  valves  cannot  be  approved,  as  the  weights 
are  apt  to  fall  off  without  warning,  the  rods  to  become  corroded 
or  be  bent  by  a  careless  workman  when  cleaning  or  scaling  the 
boiler.  Such  valves,  not  being  in  plain  sight,  cannot  be  readily 
inspected. 

The  types  of  valves  chiefly  used  are  either  those  externally 
loaded  with  dead  weight,  those  loaded  by  a  weight  on  the  arm 
of  a  lever,  or  those  loaded  by  a  spring. 

Dead-weight  valves  of  the  "Coburn"  type  (Fig.  117)  have  the 


I •"••^ 


FIG.  117. — Dead-weight  Safety-valve,  Coburn  Type. 

advantage  of  great  simplicity  and,  can  be  least  affected  by  tam- 
pering, since  they  require  so  much  weight  that  any  additional 
amount  to  seriously  overload  them  can  be  quickly  detected.  The 
high  pressure  now  in  vogue,  however,  makes  this  class  of  valve 
very  cumbersome.  They  are  more  used  in  Europe  than  in 
America. 

Lever-valves  are  loaded  by  a  weight  carried  on  the  end  of  an 
arm.  By  altering  the  position  of  the  weight,  a  greater  or  less 
load  can  be  easily  thrown  on  the  valve.  Such  valves  are  simple 
and  reliable,  but  are  more  easily  tampered  with  than  the  former, 
although  experience  has  proved  that  such  tampering  is  exceptional. 
Care  should  be  taken  with  lever-valves  to  arrange  the  point  of 


270  STEAM-BOILERS 

support  on  the  valve  and  the  fulcrum  around  which  the  arm  turns, 
in  exactly  the  same  horizontal  plane,  so  that  there  may  be  no  side 
pressure  brought  on  the  valve. 

The  problem  of  determining  the  position  of  the  weight  for  any 
desired  pressure,  is  one  of  simple  proportion.  The  load  on  the 
valve  is  equal  to  the  steam  pressure  times  the  area  of  valve. 
Neglecting  the  weight  of  the  lever,  this  load  is  to  the  weight 
inversely  as  their  distances  from  the  fixed  point  of  support. 

Spring-loaded  valves  are  now  largely  used  for  all  kinds  of 
boilers  and  are  the  only  type  adopted  for  marine  and  locomotive 
use,  since  they  are  independent  of  gravity.  This  class  of  valve 
can  be  locked  so  as  to  prevent  tampering,  and  also  can  be  easily 
operated  by  hand.  Taking  everything  into  consideration,  a  good 
spring-loaded  valve  is  probably  the  most  reliable  of  all  the  different 
types.  They  are  the  most  expensive.  Spring  valves  are  furnished 
with  lugs,  to  use  when  the  boiler  is  under  heavy  test  pressures,  in 
order  that  the  spring  may  not  be  overstrained.  The  resistance 
to  the  lift  of  the  valve  due  to  the  compression  of  the  spring  is 
overcome  by  making  the  valve  overlap  the  seat.  When  the  valve 
has  lifted,  the  steam  then  acts  on  the  full  area.  Spring  valves 
made  in  this  way  lift  higher  than  ordinary  conical  valves. 

The  area  of  a  safety-valve  is  the  area  exposed  to  the  steam 
when  the  valve  is  shut,  and  their  commercial  rating  is  based  on 
this  area. 

Valves  are  seldom  used  over  4  inches  in  diameter.  The  usual 
rule  for  size  of  valve  required  is,  for  dead-weight  or  lever-valves, 
1  square  inch  of  valve  to  every  2  feet  of  grate  area ;  and  for  spring- 
loaded  valves,  1  square  inch  of  valve  to  every  3  square  feet  of  grate. 

The  actual  area  of  opening  is  always  much  less  than  that  of  the 
valve,  and  the  greater  the  pressure  the  less  will  be  the  valve  lift. 
When  the  seat  is  coned  or  V-shaped,  the  opening  is  less  than  the 
lift  times  the  circumference,  since  the  seat  is  oblique  to  the  lift. 

The  opening  should  be  of  sufficient  size  to  discharge  all  the 
steam  that  the  boiler  can  generate.  Assuming  that  each  pound 
of  coal  can  evaporate  10  pounds  of  water,  and  let 

W  denote  the  pounds  of  steam  generated  per  second, 

g        "        "  grate  area  in  square  feet, 

c        "        "  quickest  rate  of  combustion  per  square  foot  of 
grate  per  hour, 


BOILER  FITTINGS  271 

then 

gXcXlO_gXc 
3600        360  * 

The  quantity  of  steam  that  will  escape  into  the  atmosphere 
under  pressures  usually  obtained  in  modern  practice  may  be 
estimated  thus: 

Let  w  denote  the  weight  of  steam  in  pounds  that  escapes  per 
second  per  square  inch  of  area  of  opening, 
P       "         "     absolute  boiler  pressure, 
then 


Valves  seldom  lift  as  much  as  TVinch  from  the  seat,  even  when 
made  in  the  most  approved  manner.  Ordinary  conical  valves  can- 
not be  relied  upon  to  lift  more  than  about  ^0-inch,  and  under  many 
conditions  not  so  much.  When  the  seat  is  conical,  as  is  the  most 
common,  the  area  of  opening  is  equal  to  the  circumference  of  inner 
edge  of  seat  times  the  lift  times  the  cosine  of  the  angle  to  which 
the  seat  is  bevelled. 

To  find  the  area  of  valve  required,  divide  the  value  of  W  in 
equation  (a)  by  that  of  w  in  equation  (b),  and  the  quotient  will 
be  the  area  of  opening  required.  Divide  this  area  by  the  assumed 
lift  times  the  cosine  of  the  angle  of  bevel  of  seat,  and  the  quotient 
will  be  the  circumference  of  valve.  The  corresponding  area  will  be 
the  valve  area  required. 

A  safety-valve  does  not  close  until  the  pressure  has  fallen  some- 
what below  that  at  which  it  opened  or  "  popped."  This  difference 
usually  exceeds  four  pounds. 

Safety-valve  casings  are  generally  made  of  cast-iron,  although 
they  are  sometimes  made  of  gun-metal.  The  valve  is  of  gun-metal 
or  brass,  and  the  seat  of  gun-metal  or  of  nickel  screwed  into  a 
gun-metal  base. 

In  locating  a  safety-valve,  always  place  it  as  close  to  the  boiler 
as  possible  and  avoid  all  liability  of  interference  with  the  stoppage 
of  the  connecting  pipe.  It  is  best  to  place  the  valve  at  the  boiler 
and  carry  away  the  escaping  steam  through  an  open  pipe  rather 
than  have  the  pipe  between  the  boiler  and  the  valve.  Any  pipe 
between  the  boiler  and  the  valve  should  be  as  large  as  the  area 


272  STEAM-BOILERS 

of  valve,  or,  better,  one  size  larger.  It  should  be  straight  and  self- 
draining  back  to  the  boiler. 

Fusible  Plugs  are  frequently  used  and  are  required  by  law  in 
boilers  of  sea-going  vessels.  They  are  inserted  in  the  highest  part 
of  the  heating  surface  and,  being  composed  of  an  alloy  having  a 
low  fusing  point,  melt  as  soon  as  they  become  exposed  by  lack  of 
water.  The  blast  of  escaping  steam  gives  the  alarm. 

The  plug  is  generally  made  of  composition,  with  a  fusible  metal 
centre  about  ^-inch  in  diameter.  Instead  of  an  alloy,  banca  tin 
is  a  reliable  metal.  Tin  is  not  liable  to  change  its  melting-point, 
which  is  about  443  degrees  F.  Fusible  alloys  do  not  always  work, 
especially  when  old,  as  the  melting-point  of  some  alloys  appears  to 
change  with  age.  Plugs,  therefore,  should  be  occasionally  renewed. 

The  plugs  should  always  be  screwed  into  the  boiler  from  the 
steam  or  pressure  side,  and  the  hole  containing  the  alloy  should 
be  made  tapering  to  prevent  the  metal  being  blown  out.  The  plug 
should  stand  an  inch  or  more  above  the  sheet  into  which  it  is 
fastened,  in  order  that  it  may  not  become  covered  with  scale. 

Various  forms  are  in  use  (see  Fig.  118). 

„ INSIDE  TYPES „         >- OUTSIDE  TYPES   


FIG.  118. — Various  Forms  of  Fusible  Plugs. 

Steam-gauge.  Every  boiler  should  have  connected  to  it  a  clear- 
faced  steam-pressure  gauge.  The  face  should  not  be  less  than  6 
inches  in  diameter,  and  as  much  more  as  its  height  above  the 
floor  and  the  darkness  of  the  boiler-room  may  require. 

Pressure  gauges  are  made  with  a  "Bourdon"  tube,  a  bent  tube 
having  an  elliptical  section,  which  tends  to  straighten  out  as  the 
pressure  is  applied.  The  extent  of  the  straightening  is  magnified 
by  a  system  of  levers  connecting  the  free  end  of  the  tube  with  the 
dial-pointer.  The  tubes  are  usually  of  brazed  brass,  but  are  also 
made  solid-drawn,  which  is  considered  better.  Some  gauges  are 
fitted  with  two  tubes  to  prevent  vibration  of  the  magnifying  move- 
ment, which  causes  rapid  wear.  Such  double-spring  gauges  are 
useful  in  locomotives,  fire-engines  and  portable  boilers. 


BOILER  FITTINGS  273 

The  instrument  should  be  located  at  the  water-line  to  obtain 
a  correct  reading.  If  located  above  or  below  the  water-line,  a  cor- 
rection must  be  made  for  accurate  reading,  as  in  testing.  This 
correction  is  the  weight  of  the  water-column  which  hangs  011  the 
gauge  according  to  its  connection. 

The  connecting  pipe  should  lead  direct  into  the  steam  space 
and  not  close  to  any  steam-pipe  carrying  a  flow  of  steam,  lest  the 
current  effect  the  pressure.  If  there  is  a  superheater  or  steam- 
drum,  as  in  Figs.  26  and  27,  the  steam  connection  should  be  made 
to  the  boiler  and  not  to  the  superheater,  as  the  pressure  in  the  latter 
may  fluctuate  with  the  strokes  of  the  engine.  The  connecting  pipe 
to  the  gauge  should  be  bent  to  form  a  trap  for  water,  so  that  the  hot 
steam  may  not  enter  the  instrument.  If  there  is  danger  of  freez- 
ing when  the  boiler  is  not  in  use,  a  straight  pipe  self -draining  back 
to  the  boiler  can  be  used  with  a  siphon-cock  made  for  the  purpose. 

Continuous-recording  gauges  are  made  which  record  the  pres- 
sures on  a  chart.  These  gauges  are  very  convenient  in  some  com- 
mercial works  continuously  operated. 

Water-gauge.  Every  boiler  should  have  a  glass  column  to 
show  the  water-level,  with  the  ends  connected  to  the  water  and 
steam  spaces.  These  connections  should  be  made  direct  to  the 
boiler  at  points  as  far  as  possible  from  places  where  strong  currents 
may  exist,  as  currents  or  fluctuations  in  pressure  will  cause  the 
water  to  vibrate  in  the  column.  As  a  glass  column  is  apt  to  break, 
each  connection  should  be  fitted  with  a  valve,  and  the  best  valves 
are  those  which  have  an  automatic  closing  device.  The  column 
should  be  so  set  in  the  fitting  that  steam  can  be  blown  through 
for  cleaning.  Care  should  be  taken  to  see  that  the  connecting 
pipes  are  clear,  as  scale  or  dirt  in  the  water-pipe  may  close  off  the 
connection  without  warning.  Reflex  water-gauges  are  stronger 
and  indicate  more  distinctly  than  plain  glass  gauge-tubes.  They 
are  made  with  grooved  facets  on  the  water  side  of  a  glass,  which  is 
so  set  in  a  metal  fitting  that  the  part  filled  with  water  appears 
black  and  that  with  steam  shines  with  a  silvery  lustre. 

Internal  floats  connected  to  a  dial,  like  a  steam  gauge,  cannot 
be  recommended  for  general  use,  as  the  moving  parts  are  all  con- 
cealed inside  the  boiler.  Fig.  119  shows  the  usual  water-gauge  and 
try-cock  column;  and  Fig.  120  shows  glass-protector  guards. 

Try-cocks  are  used  to  test  for  water-level.  There  are  usually 
three,  one  at  the  high-water  line,  one  at  low-water  line  and  one 


274 


STEAM-BOILERS 


midway  oetween  the  others.     When  only  two  cocks  are  used;  place 
them  about  5^  inches  apart,  and  when  three  cocks  about  4  inches. 

These  cocks  are  best  placed  directly  on  the  boiler  head  or 
shell,  but  are  often  arranged  on  the  glass  water-column  fixture. 
This  latter  plan  is  open  to  the  objection  that  any  accident  to  or 

II 


FIG.  119. — Water-gauge  and  Try-cock  Column. 

stoppage  of  piping  renders  both  means  useless  for  showing  the 
water-level,  and  the  boiler  would  have  to  be  shut  down.  A  drain 
cup  and  pipe  can  be  arranged  to  carry  off  the  drip  from  the  cocks, 
which  should  not  be  allowed  to  fall  on  the  boiler  shell  or  head. 

Some  engineers  place  more  reliance  on  the  try-cocks  than  on 
the  glass  column,  while  others  prefer  two  separate  columns  to  each 
boiler  and  no  cocks. 

Water-alarms.  These  devices  are  used  to  automatically  give 
warning  when  the  water-level  is  dangerously  low  or  high,  and  there 
are  a  number  of  makes  on  the  market. 


BOILER   FITTINGS 


275 


In  general,  internal  floats  cannot  be  approved,  as  they  are  out 
of  sight  and  difficult  to  inspect  and  keep  in  repair.  Internal  floats 
are  frequently  used  with  Cornish  and  Lancashire  boilers,  especially 
in  foreign  practice.  Such  an  apparatus  is  shown  in  Fig.  17. 

A  good  form  of  water-alarm  is  that  of  a  combined  alarm  and 


TOUGHENED  GLASS,   J  INCH  THICK 


^TOUGHENED  GLASS,  S  INCH  THICK 
FIG.  120 — Glass  Protector  Guards  for  Glass  Tube  of  Water-column. 

water-column  (Fig.  121).  The  floats  are  placed  inside  of  a  cylindri- 
cal casting,  which  is  connected  at  the  top  with  the  steam  space  and 
at  the  bottom  with  the  water  space  of  the  boiler.  These  floats 
act  on  a  small  whistle,  one  opening  it  for  low  water  and  one  for  high 
water.  The  objection  is  the  complication  and  liability  to  get  out 
of  order,  due  to  scale  and  dirt,  as  well  as  the  general  neglect  of  the 
attendant  who  is  prone  to  rely  on  the  instrument.  If  such  a  device 
be  adopted,  the  try-cocks  should  be  on  the  boiler,  and  not  on  the 
fixture,  as  then  the  boiler  could  be  operated  by  the  cocks  while  the 
column  fixture  is  shut  off  for  repair  or  cleaning. 

Every  engineer  must  rely  on  his  own  experience  whether  such 
automatic  "safety"  appliances  are  a  benefit,  and  whether  their 
adoption  more  than  offsets  their  objections. 

Manholes  and  Handholes.  Every  boiler  should  be  equipped 
with  both  manholes  and  handholes  so  located  as  to  facilitate 
inspection  and  cleaning  of  all  parts.  In  boilers  that  are  compli- 
cated by  braces,  flues  and  other  obstructions,  preventing  the 
entrance  of  a  man,  handholes  should  be  so  arranged  that  by  placing 
a  light  through  one  the  remaining  parts  can  be  seen  through 
another. 

These  openings  are  generally  elliptical  for  the  convenient 
removal  of  the  cover,  which  is  placed  on  the  inside  of  the  boiler 
in  order  that  the  steam  pressure  will  assist  in  holding  it  against  the 


276 


STEAM-BOILERS 


seat.    They  may  be  any  shape,  however,  so  as  to  fit  in  between 
flues  and  braces. 

The  standard  size  for  manholes  is  15  inches  by  11  inches,  and 
for  handholes  4J  inches  by  3  inches.  When  manholes  are  placed 
in  a  cylindrical  shell,  the  major  axis  should  be  in  the  direction  of 


FIG.  121. — Combined  High-  and  Low-water  Alarm  and  Water-column. 

the  girth,  that  the  least  amount  of  shell  shall  be  cut  longitudinally, 
which  is  the  direction  of  greatest  weakness. 

The  opening  should  be  reinforced  to  make  up  for  the  metal  cut 
out.  It  is  impossible  to  calculate  the  amount  of  reinforcement 
required,  as  the  stresses  are  so  ambiguous.  The  amount  of  com- 
pensation for  the  weakness  caused  by  the  hole  is  best  determined 
by  experience.  The  strengthening  is  usually  accomplished  by 
either  riveting  a  flat  steel  ring  piece  around  the  hole,  or  by  riveting 
a  steel  ring  flanged  inward,  or  by  flanging  the  shell  plate  itself. 
The  latter  is  the  best  method,  but  the  most  expensive,  and  incurs 
the  danger  of  internal  stresses  due  to  the  local  heat  for  flanging, 


BOILER  FITTINGS  277 

unless  the  shell  be  subsequently  annealed.  The  second  method 
is  generally  adopted  for  high-pressure  boilers,  as  it  is  stronger 
than  the  first  or  the  most  common  plan.  A  great  advantage  in 
either  of  the  flanging  methods  lies  in  the  fact  that  the  inner 
edge  may  be  planed  off  flat  when  the  manhole  is  located  on  a 
curved  sheet.  It  is  much  easier  to  maintain  a  tight  joint  with 
the  cover  when  the  contact  surfaces  are  straight  than  when 
curved.  The  stiffening  piece  may  be  made  with  an  angle-ring 
riveted  to  the  shell,  but  this  method  is  not  satisfactory,  as  it  is 
difficult  to  make  a  neat  appearance  and  obtain  a  close  and  even 
fit.  Formerly  it  was  quite  common,  especially  with  Cornish 
and  Lancashire  boilers,  to  fit  a  cast-iron  or  malleable-iron  special 
mounting,  riveted  to  the  shell,  and  to  place  the  manhole  upon  the 
top,  but  this  method  is  not  suitable  for  heavy  pressures. 

The  covers  are  made  of  cast-iron,  malleable-iron,  cast-steel,  or 
steel  plate,  the  latter  sometimes  forged  into  a  convenient  corru- 
gated section  for  strength. 

When  fastened  to  a  special  mounting,  the  covers  are  usually 
bolted  to  the  flange  of  the  mounting  with  bolts  spaced  not  over 
seven  thicknesses  of  flange  apart.  Ordinarily  the  covers  are  held 
in  place  by  yokes  or  dogs  and  bolts.  For  large  manholes  there 
should  be  two  yokes,  and  for  small  ones  and  for  handholes  one  yoke 
will  suffice.  There  is  generally  but  one  bolt  to  each  yoke.  As  the 
cover  is  on  the  pressure  side,  the  object  of  the  bolt  is  to  draw  the 
cover  up  tight.  The  feet  of  the  yoke  should  rest  on  the  boiler- 
sheet  or  stiff ening-ring,  with  its  axis  at  right  angles  to  the  major 
axis  of  the  opening. 

The  joint  between  the  cover  and  the  boiler  should  be  smooth 
and  a  true  fit.  It  is  kept  tight  by  a  gasket  of  hard  rubber,  thin 
asbestos,  or  corrugated  copper,  or  by  a  copper  wire  or  fine  lead  pipe 
laid  in  a  groove  and  squeezed  tight  by  the  pressure  of  the  bolts. 
Gaskets  cut  from  sheets  of  packing  or  rubber  are  the  simplest. 
Corrugated-copper  gaskets  make  an  excellent  joint  and  can  be 
bought  ready  made  of  standard  sizes. 

The  accompanying  Figs.*  122  and  123  illustrate  typical  man- 
holes, the  details  of  which  can  be  varied  to  suit  special  require- 
ments. 

*  See  Marine  Engineering,  June,  1899. 


278 


STEAM-BOILERS 


Grates.  The  grate  may  be  of  either  the  stationary,  shaking,  or 
mechanical-stoking  class.  Mechanical-stoking  grates  will  be  dis- 
cussed in  Chapter  X. 

The  grate  should  be  so  formed  as  to  allow  sufficient  air  to  pass 


FIG.  122. — Manhole  and  Cover  for  a  Flat  Sheet. 

through  it,  and  the  openings  should  not  be  too  large  or  the  coal  will 
fall  through  unburned. 

Provision  for  allowing  air  to  enter  above  the  grate  should  always 
be  provided,  more  especially  with  bituminous  coals  and  wood. 
For  anthracite,  the  area  of  such  openings  should  be  about  ¥|-¥  of  the 
grate  surface,  and  for  very  bituminous  coals  about  -^V  of  grate 


FIG.  123. — Manhole  and  Cover  for  a  Cylindrical  Shell. 

surface.  Intermediate  coals  should  have  a  proportionate  ratio. 
Such  liberal  proportions  are  seldom  found  in  practice.  Some 
area  can  be  provided  in  the  fire-doors,  some  over  the  doors  as  in 
Fig.  12,  and  some  in  a  split  bridge,  or  in  a  passage  through  the  bridge 
wall  as  in  Figs.  124  and  125,  but  all  must  be  equipped  with  doors 
and  dampers  so  as  to  shut  off  or  regulate  the  air-supply. 

The  distance  from  the  grate  to  under  side  of  shell  in  externally 
fired  boilers  should  be,  with  anthracite  coal,  about  24  inches  for 
grates  4  feet  long,  and  be  increased  in  proportion.  For  bituminous, 


BOILER  FITTINGS 


279 


non-caking  coals,  this  distance  should  be  increased  to  from  30 
inches  to  36  inches ;  and  for  fatty  coals  from  40  inches  to  48  inches, 
while  even  greater  heights  have  been  found  beneficial. 


FIG.  124. — Split  Bridge  with  Passage  to  Admit  Air. 

The  height  of  grate  above  the  fire-room  floor  should  be  from  18 
inches  to  26  inches,  24  inches  being  about  the  average. 


QOILER  SHELL 


FIG.  125. — Split  Bridge  with  Passage  to  Admit  Air. 

In  internally  fired    furnace-flues    these    distances    cannot    be 
realized,  but  the  larger  the  flue  the  better,  especially  with  soft 


280  STEAM-BOILERS 

coals,  and  with  small  flues  use  a  short  grate.  Grates  should  not 
be  longer  than  twice  the  flue  diameter  in  order  to  accomplish  the 
best  results. 

Stationary  grates  are  generally  made  of  cast-iron.  Cast-steel 
makes  an  excellent  and  durable  grate,  but  the  castings  are  some- 
what difficult  to  make,  as  they  are  liable  to  warp  when  cast. 

Grate-bars  are  usually  cast  in  lengths  of  24  inches,  30  inches 
and  36  inches,  consisting  of  two  or  three  bars  to  a  set  (Fig.  126). 


o 


FIG.  126.— Cast-iron  Grate-bar. 

The  bars  are  made  tapering  downward,  to  enable  the  ashes  to  drop 
clear.  The  upper  part  is  best  made  parallel  for  about  J  inch,  so 
that  the  upper  surface  may  burn  away  to  that  extent  before  the 
openings  are  increased  in  width.  The  bars  are  made  deep  that  the 
entering  air  may  be  heated,  thus  keeping  the  bars  cooler  and  pre- 
venting them  from  burning  and  twisting.  The  bars  are  usually  f- 
inch  wide  at  the  top,  tapering  to  f-inch  at  the  bottom,  and  are  from 
3  inches  to  4  inches  deep  at  the  centre.  As  depth  is  advantageous, 
the  above  amount  could  be  increased  when  there  is  plenty  of  height 
in  the  ash-pit.  The  bars  are  cast  with  distance-pieces  or  lugs  to 
keep  the  proper  spacing  and  prevent  warping.  The  tops  of  the 
bars  are  often  grooved  for  use  with  bituminous  coals.  These 
grooves  admit  air  to  all  parts  of  the  fire,  and  tend  to  prevent 
clinkers  from  attaching  to  the  bars  on  account  of  the  ashes  that 
collect  in  them. 

The  aggregate  area  of  opening  between  the  bars  should  be 
about  fifty  per  cent  of  that  of  the  grate,  but  not  less  than  forty  per 
cent  nor  in  excess  of  sixty  per  cent.  The  fatty  or  gaseous  coals 
require  a  larger  free  area  than  hard  coals.  For  very  fine  coals  and 
for  some  grades  of  cheap  coals  and  lignites,  a  perforated  plate  can 
be  used  with  advantage. 

The  width  of  opening  depends  on  the  quality  and  size  of  coals, 
hard  coals  requiring  narrower  openings  than  soft  coals.  Two  wide 
a  spacing  of  the  bars  cannot  be  used  with  the  bituminous  caking 
coals,  as  they  will  form  solid  clinkers  difficult  to  break  out. 


BOILER  FITTINGS 


281 


In  general,  the  narrower  the  bars  and  spaces  the  better,  but  on 
account  of  excessive  warping  very  thin  bars  cannot  be  used. 
The  average  proportions  are  about  as  given  in  Table  XX. 

TABLE  XX 

AIR    SPACES    AND    THICKNESS  OF  GRATE-BARS 


Size  and  Kind  of  Coal. 

Width  of 
Air  Spaces. 

Thickness  of 
Grate-bars. 

Screenings 

£in 

1 

i  to  f 
Jtof 

?h 

j 

\ 
\ 

in 

,     i 
.    < 

ch 

< 

< 
i 
t 

Anthracite   average 

"          buckwheat  

tf          pea  or  nut.  .  .. 

"          stove.. 

"          egg 

"          broken 

"          lump  

Bituminous  average                                         .    .    . 

Wood  slabs                                                        .    .    . 

"      sawdust                                .            .          .    . 

11      shavings 

Grates  often  are  set  horizontally,  but  long  grates  are  best  placed 
sloping  toward  the  rear  to  facilitate  firing.  One  inch  per  foot  is 
a  good  allowance. 

The  front  of  the  grate,  when  designed  for  bituminous  coal,  is 
often  made  solid.  This  piece  is  called  the  "dead  plate."  The 
fresh  charge  of  coal  is  thrown  on  the  dead  plate  and  allowed  to  coke 
until  all  the  hydrocarbons  have  been  volatilized  and  burned  as  they 
pass  over  the  incandescent  coal  in  the  rear.  The  charge  is  pushed 
back  on  the  open  grate  at  the  time  of  next  firing.  The  dead  plate 
is  not  regarded  so  favorably  as  formerly,  due  to  the  high  rates  of 
combustion  now  practised.  In  order  to  coke  all  the  coal  at  rapid 
rates  of  combustion  it  would  necessitate  a  great  width  of  dead 
plate  and  consequently  an  inconvenient  length  of  grate. 

Grates  should  be  so  supported  that  one  end  is  fixed  and  the 
other  free  for  expansion.  With  brick-set  boilers,  the  bearers  can 
be  built  into  the  brickwork.  With  internally  fired  boilers,  the 
proper  placing  of  bearers  is  more  difficult.  It  is  bad  practice  to 
fasten  clips  by  tap-bolts  to  a  fire-box  or  flue,  as  these  bolts  are  apt 
to  leak  and  corrode.  For  upright  vertical  boilers  a  cast-iron  plate 
suitably  shaped  and  placed  under  the  water-leg,  as  in  Figs.  13,  14, 
15  and  15a,  is  much  better.  In  furnace-flues,  a  bearer  with  wide 
tee-shaped  ends  made  to  fit  the  sides  of  flue  will  answer,  as  the  fric- 


282 


STEAM-BOILERS 


tion  will  lend  all  the  support  necessary.     In  corrugated  furnaces, 
a  half-round  steel  bent  to  fit  into  a  corrugation,  as  in  Fig.  127, 


FIG.  127. — Grate  Bearer  for  Corrugated  Furnace. 

will  be  sufficient.  When  properly  made,  there  is  no  danger  of 
the  grate  falling  with  either  of  these  latter  methods,  as  sufficient 
longitudinal  support  is  received  from  the  front  and  bridge  wall. 
In  corrugated  furnaces  the  outside  bars  must  be  specially  made 
to  fit  close  into  the  corrugations.  If  an  ash-pan  of  curved  iron 
plate  is  used  in  the  furnace-flues,  the  clips  for  bearers  can  be 
bolted  to  the  pan  without  objection. 


FIG.  128. — Plan  of  Herring-bone  Grate-bar. 

Instead  of  straight  bars,  the  herring-bone  pattern  is  frequently 
adopted  (Fig.  128).  The  angular  cross-bars  are  durable,  and 
give  freedom  for  expansion  combined  with  great  stiffness  in  the  wide 
casting.  They  are  not  so  easily  sliced  as  straight  bars,  and  are, 
therefore,  not  so  convenient  with  coals  that  clinker  badly. 


BOILER  FITTINGS 


283 


Shaking-grates  have  an  advantage  in  affording  means  to  clean 
out  the  ashes  and  dislodge  clinkers  without  opening  the  fire  door. 
This  is  the  real  base  of  the  claims  for  increase  in  economy.  They 
also  save  considerable  'manual  labor  and  are  therefore  much  liked. 
Those  forms  are  to  be  preferred  which  have  the  least  complications, 
and  which  break  up  the  fire  with  the  least  disturbance  of  the  bed 
of  coals. 

There  are  a  number  of  varieties  of  sectional  shaking-grates  on 
the  market,  and  some  of  them  are  made  self -dumping  (Fig.  129). 

OUTSIDE  BEARING  BAR 


FIG.'  129. — Shaking-grate. 

The  Ashcroft  grate  consists  of  steel  bars  of  triangular  section 
that  can  be  turned  alternately  by  a  key,  fitting  the  ends  which 
project  through  the  front  (Fir.  130).  These  bars  are  supported 


FIG.  130.— Section  of  Ashcroft  Grate-bars. 

by  bearers  spaced  about  18  inches  apart,  made  of  a  steel  strip 
set  on  edge,  with  half  circles  cut  out  to  fit  and  guide  the  grate-bars. 
The  bars  are  liable  to  warp  and  twist ;  but  as  tljey  can  be  straight- 
ened, they  should  be  made  easily  removable.  This  makes  a  very 
light  form  of  grate. 

For  burning  sawdust,  tanbark  and  similar  fuels,  a  grate-bar 
of  the  form  shown  in  Fig.  131  is  often  used. 


284 


STEAM-BOILERS 


The  Down-draft  Grate  is  a  special  design,  so  arranged  that 
the  draft  is  downward  through  the  bed  of  coals  (Fig.  132).  Below 
the  upper  grate  is  another  on  which  the  falling  particles  of  coal  are 


FIG.  131. — Grate  for  Burning  Sawdust  or  Tan-bark. 

caught  and  burned.  Beneath  the  lower  grate  is  the  ash-pit.  The 
upper  grate  is  made  hollow  and  has  a  water  circulation  so  that 
it  may  be  kept  cool  and  prevented  from  burning.  Incidentally 


FIG.  132. — Down-draft  Grate. 

this  increases  the  heating  surface.  Tests  with  certain  grades  of 
fuel  have  shown  this  downward  draft  very  effective,  and  owing  to 
the  control  that  can  be  placed  on  the  air-supply,  it  is  promising  of 
economic  results. 

After  passing  down  through  the  grate,  the  air  and  products  of 
combustion  enter  a  very  hot  combustion-chamber.     Into  this  com- 


BOILER  FITTINGS  285 

bustion-chamber  the  balance  of  air  requisite  for  combustion  can 
be  readily  admitted.  A  strong  draft  is  required,  as  the  upper 
grate  generally  is  relatively  small  in  area  and  the  rate  of  combus- 
tion correspondingly  high.  The  coal  should  be  worked  by  the  fire- 
man, in  order  to  keep  the  draft  clear,  which  involves  extra  labor. 
Therefore  the  grate  always  will  be  more  or  less  clean,  which  will 
tend  to  reduce  the  capacity  of  the  furnace  to  respond  to  a  sud- 
den demand,  as  there  will  be  no  ash  to  shake  out  in  order  to 
freshen  the  fire. 

For  a  given  boiler,  the  capacity  of  a  down-draft  grate  is  less 
than  that  of  an  up-draft  grate  of  the  usual  size,  but  more  than  an 
up-draft  grate  of  equal  area.  It  appears  from  experiments  made 
at  St.  Louis  (see  Bryan  on  Down-draft  Furnaces,  Trans.  Am. 
Soc.  M.  E.,  Vol.  XVI,  1895)  that  less  surplus  of  air  is  required  with 
this  form  of  grate  than  with  one  of  the  ordinary  type.  That 
reducing  the  grate  area  from  the  usual  proportions  showed  an 
increase  of  economy  but  caused  a  considerable  reduction  in  the 
boiler's  capacity  for  over-work. 

Ash-pit.  The  ash-pit  should  be  sufficiently  high  to  easily 
admit  the  air  required  for  combustion.  Small  ash-pit  doors  are  a 
too  frequent  fault.  In  fact  the  doors  themselves  are  sometimes 
sources  of  danger,  since  careless  firemen  will  use  them  to  check  the 
draft,  instead  of  the  damper  in  the  uptake,  and  thus  burn  out  the 
grates. 

The  height  of  the  ash-pit  may  be  as  much  as  desired  and  con- 
venient, but,  if  possible,  should  never  be  less  than  24  inches,  except 
with  very  small  boilers.  As  the  height  of  grate  above  the  fire- 
room  floor  is  fixed  by  convenience  for  charging  coal,  the  ash-pit 
may  be  sunk  below  the  floor  in  order  to  secure  increased  height. 
The  entrance  should  then  be  inclined  as  in  Figs.  11  and  12. 

Some  engineers  inject  steam  into  the  ash-pit  and  others  use  a 
tight  pan  with  water,  both  with  the  object  of  assisting  combustion. 
There  is  really  no  advantage  in  economy  beyond  the  partial  pre- 
vention of  clinkering. 

In  furnace-flues  an  ash-pan  is  often  used,  made  of  ^-inch  or 
T\-inch  iron  plate  curved  to  fit.  They  are  not  necessary  in  plain 
flues,  but  are  useful  in  the  corrugated  forms.  The  only  object  is  to 
provide  a  smooth  surface  for  raking  out  the  ashes.  Instead  of 
using  an  ash-pan,  the  corrugations  can  be  filled  flush  with  cement. 


286  STEAM-BOILERS 

When  the  ashes  are  pulled  out  of  the  pit  or  the  fire  drawn,  the 
refuse  should  not  lie  against  the  boiler  front,  as  it  will  soon  become 
corroded.  For  furnace-flue  boilers,  as  the  Cornish,  Lancashire 
and  Scotch,  there  should  be  an  iron  apron  to  protect  the  head. 
This  apron  can  be  easily  renewed. 

Fire-doors.  The  fire-doors  are  made  of  cast-iron,  cast-steel 
or  wrought-steel.  They  are  seldom  made  less  than  12  inches  high 
by  16  inches  wide.  For  very  wide  grates  two  small  doors  are 
preferable  to  one  large  one.  The  door  is  protected  on  the  inside 
by  a  liner  plate,  which  should  be  perforated  to  break  up.  into  fine 
streams  the  air  entering  through  the  door  damper.  These  liners 
are  made  of  cast-iron  and  should  be  removable  (Figs.  133  and  134). 

The  doors  can  be  made  to  automatically  shut  the  up-take 
damper  when  they  are  opened.  These  automatic  arrangements  are 
excellent  in  principle,  especially  with  forced  draft,  but  are  liable  to 
derangement  and  have  often  proved  unsatisfactory  in  practice. 

Breeching,  Uptake  and  Smoke-connection.  Unless  the 
chimney  rests  directly  on  the  boiler,  a  connection  must  be  made, 
and  this  smoke-pipe  is  called  the  breeching,  uptake  or  smoke- 
connection.  It  always  must  be  used  with  boilers  set  in  battery , 
delivering  the  products  of  combustion  into  a  common  stack. 

The  connection  when  under  the  fire-room  floor  may  be  a  brick- 
lined  conduit.  When  overhead,  it  is  made  of  steel,  either  square 
or  round  in  section.  The  former  shape  is  the  stronger  and  the 
latter  the  cheaper. 

The  connection  should  increase  in  area  as  additional  boilers 
are  connected,  otherwise  the  boiler  nearest  the  stack  will  have  the 
strongest  draft.  The  connection  should  be  free  from  all  sharp 
bends,  and  branches  should  not  be  made  directly  opposite  one 
another. 

Draft  Regulators.  The  draft  can  be  controlled  by  a  regulator 
so  that  a  constant  steam  pressure  may  be  maintained.  They  do 
not  relieve  care  of  the  fire,  but  simply  open  or  close  the  damper  as  the 
steam  pressure  falls  or  rises.  They  are  economical  and  very  useful, 
especially  in  plants  where  the  demand  for  steam  fluctuates  rapidly. 

In  the  most  common  form,  the  boiler  steam  presses  on  a  dia- 
phragm, which  is  connected  to  a  lever  that  controls  a  small  water 
valve.  If  the  steam  pressure  falls,  the  water  valve  is  opened, 
permitting  water  to  escape  from  a  hydraulic  cylinder,  thus  lower- 


BOILER  FITTINGS 


287 


8 

P  8 


^ 

I 

if 

2 


288 


STEAM-BOILERS 


ILER  FITTINGS 


289 


ing  the  plunger  and  opening  the  damper.  If  the  steam  pressure 
rises,  water  is  admitted  to  the  cylinder,  which  raises  the  plunger 
and  closes  the  damper.  When  properly  adjusted,  they  work  in 
a  very  satisfactory  manner. 

Steam-traps.  In  a  system  of  steam-piping  it  is  often  con- 
venient to  lead  the  drip-pipes  which  carry  off  the  condensed  steam 
to  a  trap.  This  trap,  while  preventing  the  escape  of  steam,  will 
discharge  the  water  and  keep  the  system  drained. 

When  the  trap  discharges  freely  into  a  cistern,  a  hot-well  or  a 
sewer,  it  is  called  a  Discharge  Trap ;  and  when  it  discharges  back 
into  a  boiler  under  pressure,  a  Return  Trap. 

There  is  a  great  variety  of  traps  on  the  market,  but  the  best 
forms  are  those  which  are  least  complicated  and  the  quickest  and 
most  readily  examined. 

A  Kieley  discharge  trap  is  shown  in  Fig.  135.     This  is  of  the 


UTLEX 


FIG.  135.— Kieley  Discharge  Trap. 

bucket  variety.  The  water  floats  the  bucket  and  closes  the  outlet. 
When  the  water  rises  and  overflows  into  the  bucket,  it  sinks  and 
the  pressure  discharges  the  contents  until  the  bucket  again  floats 
and  closes  the  outlet.  The  casing  is  so  made  that  it  can  be  re- 
moved and  expose  all  the  parts  without  disconnecting  them. 


290 


STEAM-BOILERS 


BOILER  FITTINGS 


291 


Return  traps  are  located  above  the  boiler,  about  18  inches  or 
more,  according  to  the  steam  pressure,  so  that  the  trap  may  empty 
by  gravity.  The  various  drips  are  led  to  a  manifold,  which  is  con- 
nected to  the  trap.  A  Bundy  return  trap  is  shown  in  Fig.  136. 
The  water  enters  through  one  of  the  trunnions  until  the  weight  of 
the  pear-shaped  vessel  overcomes  the  balance-weight  and  falls, 


FIG.  137. — "Potter"  Mesh  Separator — Longitudinal  Section. 


SECTION  THROUGH    A 


SECTION  THROUGH 


FIG.  137a. — Cross-section  of  Fig.  137. 

thus  opening  the  equalizing  valve  which  admits  steam  from  the 
boiler  through  the  other  trunnion.  The  equalizing  of  the  pressure 
in  the  trap  and  boiler  permits  the  water  to  flow  into  the  boiler. 
Check-valves  are  inserted  in  the  pipe  connections  to  prevent  the 
water  flowing  the  reverse  wa}r. 


292 


STEAM-BOILERS 


Separators  are  devices  placed  on  a  steam-pipe  to  remove  the 

priming  or  entrained  moisture 
carried  along  with  the  steam. 
Moisture  affects  the  steam  by 
increasing  its  density  and  its 
heat  conductivity.  It  should 
be  avoided,  therefore,  as  it 
augments  serious  losses  in  the 
piping  and  at  the  engine 
through  losses  of  heat  by  radia- 
tion and  through  changes  of 
temperature  in  the  cylinder 
walls.  Moisture  in  quantity 
may  cause  damage  by  water- 
hammer,  which  frequently  is  of 
a  serious  nature.  While  not 
essential  to  the  well  working 
of  a  boiler,  they  are  much  used 
and  a  valuable  accessory. 

Separators  are  designed  on 
two  principles,  either  by  in- 
serting a  plate  or  plates  against 
which  the  current  of  steam 
strikes, permitting  the  moisture 
to  flow  down  and  drip  off, 
while  the  gas  passes  around  the 
obstruction,  also  depositing 
more  water  by  the  change  in 
direction;  or  by  inserting  a 
spiral  passage  for  the  steam  so 
that  the  moisture  is  thrown  out 
by  centrifugal  action. 

In  Fig.    137    is    shown    a 
Potter    mesh    separator,   con- 
sisting  of   a  series  of  plates; 
and    in    Fig.  138,  a    Stratton 
separator,  operated  on  the  cen- 
FIG.  138.— Stratton  Steam-separator,     trifugal  principle. 
The  separator  should  be  located  as  close  to  the  engine  as  the 


BOILER  FITTINGS 


293 


convenience  of  the  general  arrangement  will  permit.  The  amount 
of  water  collected  in  the  separator  can  be  seen  in  the  glass  water- 
column  attached,  and  can  be  blown  out  as  required  either  into 
the  hot-well,  condenser  or  sewer  drain.  The  water  may  be  auto- 
matically removed  and  discharged  by  a  trap,  which  is  the  more 
satisfactory  plan, 


I  RETURN  DRAIN 
TO  BOILER 


FIG.  139. — Salt- water  Evaporator. 

Evaporators  are  used  to  replenish  the  supply  of  fresh  water 
for  boiler-feeding  when  salt  water  alone  is  available.  They  are 
therefore  most  used  on  shipboard  and  avoid  the  necessity  of  carry- 
ing large  storage-tanks,  thus  reducing  weight  and  increasing 
cargo  capacity. 


294  STEAM-BOILERS 

Salt  water  is  very  objectionable  when  steam  is  used  at  pres- 
sures exceeding  100  pounds  per  square  inch,  and  always  should 
be  avoided  in  water-tubular  or  sectional  boilers. 

The  evaporator  is  in  reality  a  special  form  of  boiler,  with  heat 
supplied  by  steam  from  the  main  boiler,  and  arranged  to  con- 
veniently blow  out  the  salt  as  it  deposits. 

In  Fig.  139  is  shown  a  form  of  evaporator  as  made  by  the 
James  Reilly  Repair  and  Supply  Company,  of  New  York.  It 
consists  of  a  steel  shell  containing  a  copper  piping  system  through 
which  steam  passes.  The  condensation  is  removed  by  a  trap, 
and  discharged  into  the  hot-well,  condenser  or  boiler.  An  auxil- 
iary pump  forces  water  into  the  evaporator  as  required, 
through  a  by-pass  pipe,  while  the  main  supply  circulates  through 
a  special  condenser  for  condensing  the  vapor.  The  heat  of  the 
steam  evaporates  the  salt  water,  and  the  steam  or  vapor  passes  into 
the  special  condenser,  from  which  the  fresh  water  may  be  drawn 
either  to  the  hot-well  or  the  condenser.  It  also  may  be  made  to 
pass  through  a  filter  for  furnishing  drinking-water.  If  desired 
the  steam  from  the  salt  water  can  be  passed  to  the  main  condenser 
of  the  engine,  or  to  the  low-pressure  valve-chest  of  a  triple-expansion 
engine  and  be  made  to  work  in  the  low-pressure  cylinder. 

There  are  many  forms  of  evaporators  on  the  market,  but,  like 
all  boiler  accessories,  they  should  be  simple  and  easily  cleaned  and 
repaired. 


CHAPTER  X 
MECHANICAL  STOKERS 

Classes,  Over-feed  and  Under-feed.  Advantages.  Disadvantages.  Re- 
sults Obtained  by  Use. 

Mechanical  stokers  operate  on  two  principles,  those  which 
"  over-feed,"  or  spread  the  fresh  coal  on  top  of  the  fuel  bed,  and 
those  which  "under-feed,"  or  push  the  coal  forward  beneath  the 
grate  until  it  overflows  out  on  the  grate  (Figs.  140, 141,  and  142). 
In  the  latter  operation  the  coal  is  coked  as  it  nears  the  fire  in 


FIG.  140.— The  Roney  Mechanical  Stoker. 

its  forward  and  upward  course.  Stokers  operating  with  a  revolv- 
ing endless  grate,  such  as  the  Coxe  Mechanical  Stoking  Furnace, 
are  a  special  form  of  the  over-feed  class. 

The  fuel  is  fed  through  a  hopper  and  the  rate  of  feeding  is  con- 
trolled by  a  motor.     Any  kind  of  coal,  wood  blocks,  shavings,  etc., 

can  be  used. 

295 


296 


STEAM-BOILERS 


The  claims  made  in  favor  of  mechanical  stokers  are :  A  steady 
and  uniform  supply  of  fuel;  diminished  danger  of  burning  holes 
in  the  fire,  thus  letting  air  pass  in  large  quantities  at  places  where 
the  least  amount  is  required;  smoke  prevention  due  to  continuous 
firing  in  small  quantities  and  controlled  air-supply;  reduction  of 
labor;  and  the  opportunity  to  use  coal-conveying  machinery  to 
best  advantage. 

The  objections  generally  cited  are:    Complications;    lack  of 


FIG.  141. — The  American  Mechanical  Stoker. 

durability;  lack  of  reliability  to  feed  the  fuel  evenly  over  the  fire 
grate;  and  lack  of  facility  to  force  the  fire  in  response  to  sudden 
demands. 

With  the  best  forms  of  stokers,  the  advantages  claimed  are 
more  or  less  attainable,  while  the  objections  are  not  always  realized. 
A  cheap  stoker,  however,  is  a  poor  investment.  Only  the  best 
should  be  adopted,  for  if  there  is  to  be  a  saving,  such  saving  will 
repay  the  difference  in  cost.  Stokers  should  be  operated  in  strict 
accordance  with  the  principles  of  their  design.  In  short,  the 
stoker  is  intended  to  do  a  certain  work,  and  the  attendant  should 
assist,  not  force,  it  in  the  performance  of  its  duty.  The  best  stokers 
are  those  which  are  least  complicated,  have  the  fewest  parts  to 


MECHANICAL   STOKERS 


297 


get  out  of  order  and  have  the  details  properly  worked  out  in  accord- 
ance with  good  mechanical  principles. 

Considerable  information  can  be  obtained  from  the  makers' 
catalogues,  but  such  publications  must  be  read  with  the  usual 


care. 


The  Steam  Users'  Association,  of  Boston,  has  published  some 
valuable  statistics,  from  which  the  following  has  been  taken:  * 


EVERY  ALTERNATE  GRATE  BAR  18  MOVABLE 
AND  THE  INTERMEDIATE  ONES  ARE  STATIONARY 


FIG.  142. — The  Murphy  Mechanical  Stoker. 

" Stokers  may  save  a  slight  amount  of  coal.  In  calculating 
this  from  an  evaporation  test  the  amount  of  coal  used  by  the 
stoker  engine  and  steam  blast  must  be  allowed  for.  This  may 
reach  11  per  cent. 

"Stokers  save  labor  in  large  plants,  provided  coal-handling 
machinery  is  also  installed. 

"Stokers  save  30  per  cent  to  40  per  cent  of  labor  in  very 
large  plants  (using  over  200  tons  of  coal  per  week)  20  per  cent 
to  30  per  cent  in  medium-sized  plants  (50  to  150  tons  per  week), 
and  save  no  labor  in  small  plants. 

*  Steam  Users'  Assn.  Circulars  Nos.  7  and  9.     Report  by  R.  S.  Hale. 


298 


STEAM-BOILERS 


"  Stokers  save  smoke  in  all  plants. 

"Stokers  cut  down  the  capacity,  but  not  to  any  great  extent, 
and  this  may  be  made  up  by  extra  draft. 

"Stokers,  on  an  average,  reply  to  a  sudden  call  for  steam  as 
quickly  as  hand-firing. 

"The  repairs  on  stokers  are  not  excessive  when  the  fire-room 
force  has  become  experienced  in  their  use,  but  may  be  very  heavy 
with  inexperienced  firemen.  It  is  sometimes  claimed  that  the  use 
of  stokers  makes  the  boiler  repairs  less  than  with  hand-firing. 


FIG.  142a.— Section  of  Fig.  142. 

"In  a  large  plant  stokers  will  be  advisable  if  they  make  possible 
the  use  of  a  cheaper  fuel  than  can  be  fired  by  hand.  But  it  should 
be  ascertained  that  the  cheaper  fuel  cannot  be  used  without  the 
stoker,  since  many  patent  devices  claim  and  obtain  credit  for 
savings  due  to  other  causes.  In  such  cases  there  will  be  a  saving 
in  cost  of  fuel  and  a  considerable  saving  in  labor  and  smoke,  while 
it  seems  unlikely,  judging  from  the  data  collected,  that  the  increased 
interest,  repairs,  depreciation  and  power  used  in  running  and  in 
steam  blast  will  be  enough  to  overcome  these  gains. 


MECHANICAL   STOKERS  299 

"  If  no  gain  can  be  made  by  using  a  cheaper  fuel,  still  stokers 
may  be  advisable  in  large  plants  burning  a  poor  grade  of  soft  coal. 
In  such  cases  the  saving  in  coal  will  not  be  so  great  as  when  the 
stokers  cause  a  saving  by  using  a  cheaper  fuel,  but  there  is  probably 
some  slight  saving  in  the  coal,  and  at  any  rate  a  saving  in  labor 
and  smoke.  The  interest,  repairs,  depreciation  and  steam  for 
power  and  blast  may  or  may  not  balance  these  savings. 

"  In  small  plants  stokers  will  be  seldom  advisable  unless  the 
saving  in  cost  of  fuel  will  be  quite  large,  or  unless  the  smoke 
nuisance  is  serious.  In  small  plants  the  labor  saving  is  small 
or  even  less  than  nothing,  while  the  expenses  are  no  less  in  propor- 
tion than  in  large  plants. 

"Mechanical  stoking  differs  from  hand-firing  in  that  the  firing 
is  continuous,  and  generally  in  that  the  grate-bars  are  in  contin- 
ual motion.  These  grates  are  generally  smaller  than  hand-fired 
grates. 

"The  smaller  grate  of  necessity  reduces  the  capacity.  The 
motion  of  the  grate-bars  is  continuously  disturbing  the  ash  films 
and  so  increasing  the  rate  of  combustion  per  square  foot  of  grate. 
This  largely  makes  up  for  the  small  size  of  the  grate,  when  com- 
pared on  a  long  test,  but  the  capacity  to  meet  a  sudden  call  is 
less  than  in  hand-firing,  when  the  hand-firing  is  clean.  The  stoker, 
however,  never  gets  as  dirty  as  a  hand-fired  grate  will  after  a  few 
hours,  and  the  clean  stoker  fire  responds  more  quickly  than  the 
dirty  hand  fire. 

"The  continuous  firing  has  this  effect:  There  is  a  certain 
supply  of  air  per  pound  of  coal  which  gives  the  best  results,  too 
much  or  too  little  resulting  in  a  loss.  If  the  firing  be  continuous 
the  air-supply  can  be  adjusted  to  fit  the  firing.  If  the  firing  be 
intermittent,  as  in  hand-firing,  then  the  air-supply  is  first  too 
small,  then  too  large,  and  a  loss  results.  The  more  intermittent  the 
firing  is,  the  greater  is  the  average  variation  from  the  proper  air- 
supply,  and  the  greater  is  the  loss.  The  air-supply  per  pound  of 
coal  shows  a  much  greater  tendency  to  vary  with  soft  coals  than  it 
does  with  hard.  Therefore  the  softer  the  coal,  the  more  saving  by  a 
stoker.  The  stokers  are  very  apt  to  drop  good  coal  into  the  ash- 
pit, due  to  the  continuous  motion  of  the  grate-bars,  but  as  it  is  easy 
to  make  arrangements  for  catching  and  refining  this  coal,  this  is 
unimportant." 


CHAPTER   XI 
ARTIFICIAL   DRAFT 

Advantages.  Disadvantages.  Classification.  Selection  Depends  on 
Local  Conditions.  Boiler  Must  be  Suited  to  Draft.  Vacuum  and  Plenum 
Systems  Compared.  Economy.  Intensity.  Jet  in  the  Stack.  Jet  under 
the  Grate.  Fans.  Power  Required.  Closed  Ash-pit.  Closed  Fire-room. 
Induced  Draft. 

Artificial  draft  is  steadily  growing  in  favor  with  steam-users. 
Through  its  aid  the  steaming  capacity  of  a  boiler  plant  can  be 
increased;  the  necessity  for  a  tall  stack  or  chimney  dispensed 
with;  a  high  economy  obtained  (under  proper  conditions)  due 
to  increased  furnace  temperature,  produced  by  a  more  rapid  rate 
of  combustion  and  a  reduced  amount  of  air-supply  in  proportion 
to  the  fuel  consumed;  low  grades  of  coal  or  cheap  fuels  burned; 
and  positive  control  of  the  furnace  maintained  so  as  to  suit  changes 
in  operation  or  weather.  The  chief  disadvantages  are  liability  to 
injure  the  boiler  due  to  careless  manipulation;  cost  of  operation, 
maintenance  and  repair;  extra  complications,  and  risk  of  derange- 
ment. 

The  costs  for  interest  and  maintenance  of  a  stack  necessary 
to  produce  a  natural  draft  of  equal  intensity  will  offset  in  a  large 
measure  (and  sometimes  entirely)  the  cost  of  operating  an  artificial- 
draft  system. 

An  artificial-draft  system  can  be  designed  to  consume  the 
fuel  either  at  a  low  or  a  high  rate.  In  the  latter  case  the  system 
is  commonly  known  as  forced  draft,  and  it  was  for  this  purpose 
originally  intended. 

Artificial  drafts  are  best  classified  into  "jet  drafts"  and 
"mechanical  drafts."  Mechanical  drafts  are  again  subdivided 
into  " forced  draft"  and  "induced  draft."  With  forced  draft  the 
air  is  forced  through  the  furnace  by  mechanical  means,  and  with 

300 


ARTIFICIAL  DRAFT  301 

induced  draft  the  air  is  sucked  through  the  furnace  and  the 
products  of  combustion  are  discharged  into  the  stack  by  mechan- 
ical means.  Considerable  information  on  various  forms  of  mechan- 
ical draft  can  be  obtained  from  a  catalogue  publication  entitled 
Mechanical  Draft,  issued  by  the  B.  F.  Sturtevant  Company, 
Boston,  Mass. 

In  general,  it  is  not  possible  to  state  which  system  of  artificial 
draft  is  the  better,  or  which  should  be  adopted.  So  many 
considerations  have  to  be  taken  into  account,  that  each  case 
must  be  worked  out  and  settled  on  its  merits.  While  a  system 
of  artificial  draft  has  attractions,  there  are  always  surrounding 
conditions  which  have  their  influence  on  the  selection  of  the  draft 
problem,  that  can  neither  be  overlooked  nor  undervalued. 

Artificial  drafts  produce  either  a  partial  vacuum  or  a  plenum 
in  the  furnace.  It  is  a  mooted  question  which  system  is  the  better, 
so  much  depending  on  installation  considerations.  However, 
the  induced  or  partial  vacuum  systems  do  not  appear  to  have  so 
marked  a  tendency  to  burn  holes  in  the  fire  and  produce  blow- 
pipe effects. 

The  jet  drafts  have  not  proved  as  economical  as  the  mechan- 
ical drafts,  while  between  the  various  forms  of  mechanical  draft 
sufficiently  reliable  results  have  not  been  obtained  to  make  any 
fair  comparison.  Whatever  may  be  the  difference  it  is  certainly 
not  great. 

When  artificial  draft  is  decided  upon,  the  boiler  must  be  suited 
to  the  high  temperatures,  have  sufficient  heating  surface  to  absorb 
the  heat  from  the  gases  and  have  a  strong  and  effective  circulation. 
Some  boilers  will  often  do  well  with  a  natural  draft,  but  leak  under 
an  artificial  draft  on  account  of  the  rapid  changes  in  temperature 
produced  when  the  fire-door  is  opened.  The  expanded  tube  ends 
of  fire-tubular  boilers  are  frequently  thus  affected,  and  ferrules 
have  to  be  used.  These  ferrules  may  prevent  a  continuance  of 
the  leak,  but  usually  do  not  remove  the  cause  of  the  trouble. 

The  strength  or  intensity  of  the  draft  is  expressed  in  "  inches 
of  water"  or  in  " ounces  per  square  inch,"  with  both  the  vacuum 
and  plenum  systems.  It  is  usually  measured  at  the  base  of  the 
stack,  but  sometimes  in  the  ash-pit  and  in  the  furnace.  "  Inches 
of  water"  expresses  the  difference  in  height  of  the  two  columns  of 
water  in  a  manometer  or  U-shaped  tube,  one  end  being  exposed 


302 


STEAM-BOILERS 


to  the  draft  and  the  other  to  the  atmosphere.  "Ounces"  ex- 
presses the  weight  of  this  height  of  water  reduced  to  that  unit  per 
square  inch. 

Steam  Jet  in  the  Stack.  This  method  is  not  economical, 
as  the  amount  of  steam  expended  is  large.  Under  some  conditions, 
as  in  the  locomotive  or  fire-engine,  it  is  necessary,  since  with  present 
designs  no  other  method  has  proved  so  commercially  good.*  The 


FIG.  143. — Bloomsburg  Jet  in  Stack. 

jet  also  is  extremely  useful  when  steam  has  to  be  raised  quickly, 
or  in  providing  for  sudden  calls  for  increase  of  steam  during  short 
periods. 

The  apparatus  is  simple,  very  light,  easily  arranged,  not  liable 
to  derangement  and  very  effective  in  producing  a  moderate  draft. 
It  consists  of  a  jet  or  of  a  pipe  with  perforations,  placed  at  the  base 
of  the  stack,  so  that  the  jet  or  jets  of  steam  are  discharged  upward, 
thus  causing  a  flow  of  the  gases  in  the  stack  independent  of  their 
temperature  (Figs.  143  and  144). 

The  steam  connection  to  the  jet  should  be  made  direct  to  the 


*  With  these  engines  there  is  available  exhaust  steam  at  high  pressure, 
and  a  boiler  relatively  small  to  the  size  of  the  engine  may  be  used  to  advantage 


ARTIFICIAL   DRAFT 


303 


boiler  and  not  to  any  steam-pipe.  The  size  of  pipe  required  de- 
pends on  local  conditions,  but  ordinarily  a  1-inch  or  a  IJ-mch 
pipe  is  all  that  is  necessary.  The  pipe  should  be  led  direct  to  the 
jet  and  be  fitted  with  a  stop- valve  easily  controlled  from  the  fire- 
room  floor. 

A  jet,  formed  from   1-inch  pipe,  can  consist  of  a  cross,  of  a 


STEA 


FIG.  144. — Ring  Jet  in  Stack. 

ring  or  of  a  series  of  rings  arranged  conically,  all  having  holes  (or 
slots)  about  TVor  J-inch  in  diameter  on  the  upper  -side  only.  A 
number  of  small  holes  well  distributed  will  be  more  effective  than 
one  large  hole  of  equal  area.  When  not  in  use  these  pipes  do 
not  offer  any  material  resistance  to  the  ordinary  draft  (Fig.  144). 

The  jet  may  be  produced  by  the  exhaust  steam  from  the  engine, 
as  hi  locomotives.  In  such  cases  of  exceptionally  strong  blasts, 
the  vacuum  may  amount  to  from  4  to  8  inches  of  water. 


304 


STEAM-BOILERS 


Steam  Jet  under  the  Grate.  A  jet  under  the  grate  can  be 
arranged  to  produce  a  powerful  draft  by  forming  an  air-pressure 
in  the  ash-pit.  It  has  a  stronger  tendency  to  burn  holes  in  the 
fuel  than  the  jet  in  the  stack.  The  entering  steam  heats  the  air 
which  it  draws  in  by  inspiration  through  a  suitable  opening  sur- 
rounding the  jet,  and  also  forms  water-gas  with  the  incandescent 


FIG.  145. — Beggs'  Argand  Steam-blower. 

fuel.  The  steam  also  tends  to  prevent  the  formation  of  clinkers 
and  thus  assists  combustion. 

This  system  of  forcing  the  fires  can  be  readily  attached  to 
boilers  which  are  found  to  be  small  for  their  requirements,  and  is 
especially  useful  under  boilers  which  need  forcing  for  short  periods 
only.  Fig.  145  shows  a  form  of  jet-blower  for  a  brick-set  boiler, 
and  Fig.  146  for  a  furnace-flue. 

Fans.  Fans  are  used  to  mechanically  control  the  currents  of 
air,  so  that  the  intensity  of  the  draft  may  be  varied  at  the  will  of 
the  operator  and  be  independent  of  all  foreign  conditions. 

The  fans  most  used  are  of  the  centrifugal  or  peripheral  dis- 
charge type.  The  velocity  of  air  discharged  is  practically  the 


ARTIFICIAL   DRAFT 


305 


same  as  that  of  the  tips  of  the  blades  and  the  pressure  of  the  air 
will   correspond   to   that   velocity.     The   work   performed   is   ex- 


ooooooooo 

ooooooo 

ooooo 


FIG.  145a.— Section  of  Fig.  145. 

pressed  by  the  product  of  that  pressure  times  the  distance  through 
which  it  acts.     Thus: 

Let  W  denote  the  work  performed  in  foot-pounds  per  second, 
p     "        "   pressure  per  square  foot  in  pounds, 
a      "         "   area  of  discharge  in  square  feet, 
v     "        "   velocity  in  feet  per  second, 
d     "        "    density  of  a  cubic  foot  of  air  in  pounds  =  0.0764 

pounds  at  60  °  F., 
h     "        "    head  in  feet, 


then 


£,     and    p— S-; 


W=pav= 


adv3 


306 


STEAM-BOILERS 


Since  the  fan  has  a  working  efficiency  of  about  fifty  per  cent, 
the  driving  mechanism  should  develop  a  power  of  twice  the  value 
of  W.  For  the  proper  size  of  fan  to  use  under  fixed  conditions, 
the  manufacturers  should  be  consulted.* 

A  certain  quantity  of  air  is  required  to  support  combustion. 
From  the  formula  it  will  be  noted  that  the  volume  varies  as  the 


STEAM 


FIG.  146. — Beggs'  Argand  Blower,  arranged  for  a  Furnace-flue. 

velocity,  the  pressure  as  its  square,  and  the  work  as  the  cube. 
The  best  efficiency  therefore  is  obtainable  with  a  fan  giving  the 
volume  required  at  as  low  a  pressure  as  may  be  suitable.  Also,  the 
fan  should  be  designed  to  comply  with  the  exact  conditions  under 
which  it  is  to  operate.  If  the  air  is  heated  before  it  enters  the 
fan,  then  the  fan  should  be  designed  for  use  with  hot  air  in  order 
to  save  all  the  driving  power  possible. 

The  fan  can  be  arranged  to  operate  on  a  plenum  system  by 
having  a  closed  ash-pit  or  a  closed  fire-room,  or  on  a  vacuum 
system  by  sucking  the  products  of  combustion  through  the  boiler 

*  In  Appendix  B,  a  method  is  given  for  calculating  the  capacity.and  horse- 
power of  peripheral  discharge  fans. 


ARTIFICIAL  DRAFT  307 

and  discharging  them  into  the  stack,  generally  called  "induced 
draft." 

Closed  Ash-pit  System.  The  fan  in  this  case  forces  the  air 
into  the  ash-pit,  all  openings  from  which  are  closed,  so  that  the  air 
can  only  escape  through  the  grate. 

There  is  a  strong  tendency  to  burn  holes  in  the  bed  of  fuel  by 
local  combustion.  The  air  then  escapes  through  these  holes  with- 
out prope  ly  performing  its  object.  As  a  check  to  this  tendency, 
the  entering  air  should  be  distributed  as  much  as  possible,  according 
to  the  design  of  the  ash-pit. 

This  is  a  very  simple  arrangement  and  one  always  easy  to 
install.  Economy  is  increased  if  the  air  is  heated  previous  to 
its  entrance  into  the  ash-pit. 

If  the  blast  is  strong  and  not  shut  off  before  opening  the  fire- 
door,  the  flames  are  apt  to  blow  out.  Automatic  devices  to  control 
the  draft  can  be  attached  to  the  doors,  some  of  which  work  well,  but 
all  are  liable  to  derangement,  especially  those  under  the  severe 
service  of  marine  boilers.  The  blast  should  be  such  as  to  give  the 
required  volume  of  air  without  relying  on  excessive*  pressure  or 
velocity,  a  fault  too  common  in  many  plants. 

This  system,  however,  is  dirty,  as  the  dust  and  ashes  are  blown 
outward  unless  a  tight  front  is  provided.  When  properly  installed 
and  proportioned  (with  furnace-flue  boilers  this  is  often  difficult 
to  accomplish)  the  closed  ash-pit  is  probably  the  most  generally 
satisfactory  system  of  mechanical  draft. 

Closed  Fire-room  System.  With  this  system  the  boiler  is 
set  in  an  air-tight  fire-room,  and  the  air  blowrn  in  so  as  to  maintain 
the  required  pressure.  The  air  escapes  into  the  ash-pit  and 
through  the  grate.  Entrances  into  the  fire-room  must  be  pro- 
vided with  double  doors  or  air-locks,  which  complicate  the  plant 
for  stationary  purposes.  The  system,  therefore,  is  hardly  practi- 
cable for  large  boiler-rooms,  and  is  chiefly  limited  to  marine  use. 

This  system  also  has  a  tendency  to  burn  local  holes  in  the  fuel, 
but  in  a  somewhat  lesser  degree  than  is  found  with  the  closed  ash- 
pit, due  to  the  better  and  more  even  distribution  of  the  air.  The 
system  is,  however,  free  from  the  annoyance  of  dirt,  since  all  leak- 
age is  inward.  When  the  fire-door  is  opened  the  cold  air  rushes 
in  and  has  an  injurious  effect  on  the  hot  boiler  plates.  This  can 
be  remedied  by  automatic  devices  attached  to  the  fire-door,  so 


308 


STEAM-BOILERS 


that  when  open  they  close  a  damper  in  the  uptake  or  breeching. 
These  attachments  do  not  always  work  satisfactorily.  The  same 
effect  is  attained  by  training  the  fireman  to  close  the  damper  by 
hand  before  opening  the  door,  although  a  trained  man  cannot 
always  be  implicitly  trusted. 

Both  the  closed  ash-pit  and  closed  fire-room  systems  tend 
to  cause  leaks  between  the  tubes  and  tube-sheets  of  fire-tubular 
boilers.  This  difficulty  is  partly  obviated  by  the  use  of  pro  tec  t- 


FIG.  147. — Induced  Draft — Ellis  and  Eaves'  System. 

ing  ferrules.  The  tube-sheet  is  often  made  too  stiff,  so  that  leaks 
are  caused  by  want  of  flexibility  to  let  it  accommodate  itself  to  the 
expansion  and  contraction  of  the  tubes.  This  expansion  and  con- 
traction is  considerable  and  sudden  with  mechanical  drafts  due 
to  the  inrush  of  cold  air  through  the  open  fire-door.  As  a  rule 
the  tube-sheet  cannot  be  too  flexible,  the  only  limitation  being 
safety. 

Induced  Draft.  In  this  case  the  fan  is  so  located  as  to  suck 
the  products  of  combustion  through  the  boiler,  by  having  the  flue, 
uptake  or  breeching  lead  to  the  inlet  of  the  fan.  The  fan  then 
discharges  back  into  the  stack.  This  arrangement  is  generally 


ARTIFICIAL   DRAFT  309 

designed  with  a  by-pass  direct  to  the  stack,  which  can  be  used  in 
case  of  accident  or  when  mechanical  draft  is  not  required.  Fig. 
147  illustrates  a  system  of  induced  draft. 

The  operation  of  this  system  closely  resembles  the  effects 
produced  by  chimney  draft,  only  it  is  much  more  intense  and 
capable  of  greater  range.  The  objection  is  the  deterioration  of 
the  fan  and  fan  journals,  caused  by  having  to  handle  the  hot  gases, 
but  many  improvements  have  lately  been  made.  This  system  has 
the  least  tendency  to  blow  holes  in  the  fire,  and  it  will  therefore 
maintain  a  more  uniform  combustion  over  the  grate. 

By  simple  arrangements  this  system  readily  adapts  itself  to  the 
heating  of  both  the  air  and  feed-water,  since  they  can  be  warmed 
by  the  heat  in  the  gases  without  affecting  the  draft  beyond  inter- 
posing a  slight  frictional  resistance,  which  can  be  reduced  to  a 
minimum  by  careful  designing.  Such  heaters  also  reduce  the 
temperature  of  the  gases  before  they  have  to  enter  the  fan. 


CHAPTER  XII 
INCRUSTATION 

Scurf.  Fur.  Sludge.  Scale.  Conductivity.  Solid  Matter  in  Water. 
Analysis  of  Scales.  Behavior  of  Lime  and  Magnesia  Salts.  Scale  Pre- 
vention. Blowing-off.  Chemical  Agents.  Mechanical  Agents.  Galvanic 
Agents.  Surface-condensing.  Heating  and  Filtering.  Internal  Collecting 
Apparatus.  Manual  Labor. 

EVEN  with  pure  waters,  a  certain  amount  of  incrustation  will 
collect  on  the  inside  of  steam-boilers.  This  incrustation  is  called 
" scale,"  " scurf,"  "fur"  or  "sludge,"  according  to  the  character 
of  its  formation. 

When  this  scale  is  thin,  not  exceeding  &  inch,  it  frequently  acts 
as  a  preventer  of  corrosion  with  waters  that  readily  attack  the 
metal.  When  it  collects  in  thicker  quantities,  the  plates  become 
overheated  and  the  water  spaces  choked.  There  are  few  satis- 
factory tests  on  the  obstruction  to  the  passage  of  heat  by  scale. 
When  hard  and  dense,  it  offers  greater  resistance  than  when  porous. 
More  depends  on  the  quality  than  on  thickness  as  a  barrier  to  the 
transfer  of  heat.  This  loss  of  heat  is  especially  great  when  the 
deposits  are  of  an  oily  character.  The  Devonport  experiments, 
March,  1893,  carried  out  by  the  British  naval  authorities,  showed 
a  loss  of  11  per  cent  in  efficiency  due  to  a  thin  coating  of  grease 
alone.* 

The  tendency  to  cause  local  overheating  is  greatest  with  irregu- 
lar deposits  of  varying  thickness.  This  overheating  is  aggravated 
by  the  presence  of  oil  and  grease,  which  assist  in  making  these 
irregular  deposits.  In  fact  a  piece  of  greasy  waste  left  in  a  boiler 
will  cause  a  bulging  crown  sheet  as  quickly  as  a  comparatively 
thick  formation  of  scale  uniformly  distributed. 

The  selection  of  type  of  boiler  to  be  adopted  is  often  dependent 
upon  the  quality  of  feed-water  available.  With  hard  or  bad- 

*  Transactions  Am.  Soc.  Naval  Engineers,  Vol.  IV,  1895,  page  782.  . 

310 


INCRUSTATION  311 

scaling  waters,  the  boiler  should  be  of  a  type  that  can  be  quickly 
cleaned  and  examined.  When  bad  water  only  is  available,  then 
the  simplest  type  of  boiler  is  to  be  preferred,  even  though  less 
efficient  in  evaporating  power. 

Nearly  all  waters  contain  solid  matters  in  solution,  which 
become  precipitated  by  elevation  of  temperature  and  are  left  in 
the  boiler  when  the  water  is  evaporated.  This  deposit,  unless 
removed  from  time  to  time,  will  collect  on  the  hot  surfaces  'and, 
becoming  baked,  will  form  incrustation. 

The  quantity  of  matter  thus  held  in  solution  is  generally  be- 
tween 20  and  40  grains  per  gallon,  but  often  exceeds  200  grains. 
To  appreciate  the  effect,  imagine  a  boiler  evaporating  3000  pounds 
of  water  per  hour.  This  means  an  evaporation  at  the  end  of  four 
weeks,  of  six  days  of  ten  hours  each,  of  720,000  pounds,  or  86,746 
gallons.  Assuming  the  water  to  contain  20  grains  per  gallon, 
this  amount  would  carry  into  the  boiler  and  leave  as  scale 
1,734,920  grains,  or  247.8  pounds.  Taking  the  specific  gravity 
of  the  scale  as  3,  this  quantity  would  be  equivalent  to  1.32  cubic 
feet,  or  enough  to  cover  750  square  feet  of  heating  surface  with 
scale  0.02 112-inch  thick,  or  over  ^-inch  per  year.  In  addition 
to  the  substances  in  solution,  nearly  all  waters  carry  clay  and  other 
earthy  matters  in  suspension,  which  will  greatly  increase  the  above 
figures. 

The  quantity  of  solid  matter  contained  in  any  water  is  less  of 
an  indication  of  its  fitness  for  boiler  use  than  the  quality  of  such 
matter.  Thus  a  given  quantity  of  such  salts  as  carbonate  or 
chloride  of  sodium  would  be  of  small  moment  compared  to  an 
equal  quantity  of  salts  of  lime.  It  is  unfortunate,  however,  that 
the  most  available  waters  usually  contain  the  latter  salts,  while 
the  former  are  the  exception. 

Most  waters  contain  sulphate  of  lime,  bicarbonate  of  lime 
and  carbonate  of  magnesia,  together  with  other  impurities  of 
lesser  importance,  such  as  iron,  soda,  silica,  alumina  and  organic 
matter.  These  impurities  are  deposited  in  the  following  order: 
First,  carbonate  of  lime;  second,  sulphate  of  lime;  third,  salts 
of  iron  and  magnesia;  forth,  silica,  alumina  and  organic  matter; 
fifth,  chloride  of  sodium  (common  salt). 

When  formed,  boiler  scales  will  differ  very  widely  in  their 
chemical  analyses.  As  an  example,  however,  the  following  analyses 


312 


STEAM-BOILERS 


by  Professor  Lewes  may  be  taken  as  illustrative  of  three  kinds  of 
water. 


BOILER    SCALE 


River. 

Brackish. 

Sea. 

Calcium  carbonate  

75.85 
3.68 
2.56 
0.45 
7.66 
2.96 
3.64 
3.20 

43.65 
34.78 
4.34 
0.56 
7.52 
3.44 
1.55 
4.16 

0.97 
85.53 
3.39 
2.79 
1.10 
0.32 
Trace 
5.90 

Calcium  sulphate  

Magnesium  hydrate 

Sodium  chloride 

Silica 

Oxides  of  iron  and  alumina 

Organic  matter 

Moisture 

100.00 

100.00 

100.00 

Bicarbonate  of  lime  is  held  in  solution  by  an  excess  of  carbonic 
acid.  As  the  water  becomes  heated  this  carbonic  acid  is  driven 
off,  and  carbonate  of  lime  falls  as  a  precipitate,  so  that  under  a 
temperature  of  about  212  degrees  F.  it  is  scarcely  soluble,  and  is 
said  to  be  insoluble  at  290  degrees  F.  Sulphate  of  lime  also  be- 
comes less  soluble  as  the  temperature  rises  above  100  degrees  F., 
and  is  said  to  be  insoluble  at  290  degrees  F. 

These  two  salts,  therefore,  are  always  precipitated  in  the 
boiler  when  the  pressure  reaches  about  43  pounds  above  the 
atmosphere. 

Carbonate  of  magnesium  behaves  in  a  similar  manner,  but  it  is 
generally  found  in  very  much  smaller  quantities. 

The  carbonates  of  lime  and  magnesium  deposit  in  a  fine  white 
powder,  making  a  more  or  less  whitish  sludge.  These  particles 
are  so  light  as  to  be  often  carried  by  the  steam  into  the  pipes  and 
even  into  the  engine.  These  carbonates  will  remain  as  a  soft  sludge 
for  some  time,  but  will  finally  become  hard  under  the  baking  action 
of  the  heat,  as  is  often  the  case  when  boilers  are  blown  off  while  hot. 
The  sulphate  of  lime,  however,  precipitates  so  as  to  form  an 
amorphous  crust,  which  becomes  hard  under  the  action  of  the  heat. 

On  becoming  insoluble,  all  the  precipitates  remain  for  a  time 
in  suspension,  and  are  carried  around  with  the  convection  and 
ebullition  currents  until  finally  they  settle  on  the  plates  and  tubes 
in  the  quieter  parts  of  the  boiler.  After  ebullition  ceases,  they  of 
course  settle  on  all  parts  of  the  heating  surface.  The  mouth 
of  the  feed-pipe  often  becomes  badly  furred,  since  it  forms  a  quiet 


INCRUSTATION  313 

place  for  the  precipitate  to  lodge.  Also  the  end  of  the  blow-off 
may  become  choked  for  the  same  reason.  The  feed-pipes  may 
become  choked  by  the  deposit  forming  as  the  fresh  feed  becomes 
suddenly  heated,  thus  closing  the  pipe  and  preventing  further 
entrance. 

When  oil  or  grease  is  present  in  the  boiler,  a  sticky,  heavy 
paste  is  formed  which  falls  and  fastens  to  the  nearest  surfaces, 
where  it  is  quickly  baked  hard  into  a  firm  scale. 

The  fracture  of  a  piece  of  boiler  scale  usually  exhibits  a  series 
of  layers  varying  in  thickness  and  color,  and  the  fracture  may  be 
partly  crystalline,  but  is  generally  amorphous  in  character.  Be- 
tween the  layers  is  often  found  soft  strata  of  earthy  matters,  prob- 
ably deposited  while  the  boiler  was  not  steaming. 

The  surface  of  the  incrustation  next  to  the  metal  is  often  black, 
while  the  surface  of  the  metal  is  soft  and  corroded.  This  is  due 
to  the  action  of  the  iron  salts  and  chloride  of  magnesium  when 
present. 

Chalybeate  waters  usually  are  highly  injurious,  and  these  salts 
of  iron  are  detected  by  the  reddish  color  of  the  water  as  it  leaks 
out  through  the  cracks  in  the  scale. 

Scale  Prevention.  Pure  water,  of  course,  should  be  used, 
but  as  this  is  not  always  possible,  the  following  treatments  will 
delay  the  formation  of  the  scale  and  facilitate  its  removal. 

First — Blowing  off  a  portion  of  the  water  at  regular  intervals, 
with  more  or  less  frequency  as  the  water  is  more  or  less  bad. 

This  is  always  an  easy  method  and  consequently  one  of  the 
most  common  practised.  Many  land  boilers  have  only  one  blow- 
off,  and  that  at  the  bottom.  Its  effect  is,  therefore,  not  general. 
In  order  to  broaden  the  effect  of  the  bottom  blow,  the  pipe  is 
sometimes  extended  along  the  bottom  of  the  boiler  and  this  ex- 
tension part  is  perforated.  With  this  arrangement  the  blow-off 
should  be  operated  often  enough  to  keep  the  pipe  free  from  furring. 
If  the  water  is  very  bad  in  scale-forming  qualities,  this  internal 
pipe  cannot  be  recommended. 

Boilers  should  have  also  a  surface  or  scum  blow,  which  will 
remove  some  of  the  lighter  particles,  such  as  carbonates  of  lime 
and  magnesium,  oil  and  grease.  The  internal  end  of  the  surface 
blow  is  frequently  fitted  with  a  bell  or  trumpet-shaped  mouth- 
piece. When  the  internal  arrangements  of  a  boiler  are  complicated, 


314  STEAM-BOILERS 

greater  difficulty  is  experienced  in  washing  and  cleaning  it  out, 
and  such  complications  often  are  more  objectionable  than  the 
good  they  may  do  in  freeing  from  scaling  matter. 

Blowing  off  will  not  prevent  scale,  but  its  use  may  delay  a 
thick  formation  and  the  frequent  shutting  down  of  the  boiler  for 
a  more  perfect  cleaning.  The  quantity  of  hot  water  wasted  by 
blowing  out  creates  an  expense,  which  in  some  instances  would 
repay  the  introduction  of  some  more  improved  method  of  purifi- 
cation. 

Blowing  off  is  most  effective  when  the  impurities  are  uniformly 
distributed,  as  the  chloride  of  sodium  in  sea  water.  On  the  other 
hand,  heavy  precipitates  are  less  affected  by  blowing  off  a  portion 
of  the  water,  and  in  consequence  it  is  better  with  them  to  blow 
off  more  frequently  and  less  irr  quantity  at  each  time.  Thus,  for 
extracting  magnesium  and  lime  salts,  the  blows  are  opened  in  many 
instances  once  an  hour,  while  only  ten  to  twenty  gallons  are  blown 
out  at  a  time. 

Second — Introduction  of  Chemical  Agents  to  dissolve  the  scale. 
A  great  variety  of  chemical  agents  have  been  used  with  varying 
results. 

The  one  most  commonly  used,  being  both  the  cheapest  and  the 
most  effective  for  general  results,  is  the  common  soda  of  commerce, 
bicarbonate  of  soda.  It  acts  well  in  preventing  and  removing 
scale  resulting  from  both  the  carbonate  and  sulphate  of  lime.  The 
reactions  are  as  follows :  The  soda  and  lime  exchange  their  acids, 
forming  sulphate  of  soda  and  carbonate  of  lime.  The  sulphate  of 
soda  is  very  soluble,  while  the  carbonate  of  lime,  freed  from  all  excess 
of  carbonic  acid,  precipitates  as  a  light,  flocculent  precipitate  and 
will  not  form  a  hard  crust  unless  allowed  to  bake.  The  bicarbonate 
of  lime  in  the  feed-water  is  in  like  manner  precipitated,  since  any 
free  soda  unites  readily  with  the  freed  carbonic  acid.  This  car- 
bonic acid,  taken  by  the  carbonate  of  soda,  is  again  liberated  by 
the  heat  and  the  soda  is  free  to  act  once  more. 

The  soluble  sulphate  of  soda  and  the  deposited  carbonate  of 
lime,  which  is  in  the  form  of  sludge,  can  be  blown  out  from  time  to 
time,  according  to  the  quantity  formed;  or  in  case  of  large  quan- 
tity, the  carbonate  of  lime  can  be  washed  out  after  the  boiler  has 
been  allowed  to  cool  slowly  and  gradually.  Since  the  precipitate 
of  carbonate  of  lime  is  light  and  flocculent,  large  quantities  float  as 


INCRUSTATION  315 

a  scum  when  the  boiler  is  quiet,  and  much  of  it  may  then  be  re- 
moved through  the  surface  blow. 

If  the  precaution  of  cooling  off  the  boiler  slowly  be  not  attended 
to,  or  if  the  boiler  be  blown  off  while  the  shell  and  setting  are  still 
hot,  the  sludge  may  become  baked  hard,  since  it  is  always  accom- 
panied wi^h  more  or  less  of  the  sulphate  of  lime. 

It  is  found  in  practice  that  a  small  quantity  of  soda  will  act 
with  good  results  on  large  quantities  of  feed.  If  soda  be  introduced 
in  too  large  a  quantity,  it  is  apt  to  promote  priming  with  all  the 
dangers  as  well  as  the  inconveniences  that  accompany  it. 

The  best  method  is  to  connect  the  feed-pump  or  injector  to  the 
Boda-tank,  so  that  at  regular  intervals  a  supply  of  soda  can  be 
drawn.  The  proper  amount  is  determined  in  each  case  by  experi- 
ence, but  ordinarily  varies  between  one  and  two  pounds  per  day 
for  the  average  boiler.  The  least  quantity  that  is  effective  is  all 
that  is  required. 

The  soda  does  not  injure  the  boiler  unless  it  is  impure  and 
contains  acids.  Soda  will  neutralize  the  acids  in  the  feed-water 
and  will  greatly  limit  its  natural  corrosive  action.  Soda  will  also 
dissolve  any  grease  that  may  be  in  the  boiler,  and  it  is  often  used 
in  new  boilers  to  cut  the  oil  left  from  the  process  of  manufacture. 
Both  grease  and  soda  encourage  priming,  so  when  grease  is  present 
a  frequent  use  of  the  surface  blow  is  recommended. 

Besides  soda  bicarbonate,  other  chemical  agents  are  used,  but 
few  with  such  generally  good  results  and  many  with  more  or  less 
injurious  action  on  the  boiler  and  its  fittings.  Such  other  agents 
are  soda  ash  (an  impure  form  of  the  carbonate),  caustic  soda,  pot- 
ash, chloride  of  barium,  tannic  acid,  sal  ammoniac  and  compounds 
of  arsenic. 

Third—Introduction  of  Mechanically  Acting  Agents.  A  great 
variety  of  substances  can  be  introduced  into  boilers  with  the 
object  of  coating  the  particles  of  deposit,  thereby  decreasing  their 
cohesion  and  adhesion,  thus  preventing  them  from  forming  into 
a  hard  mass. 

The  substances  act  either  by  coating  the  particles  with  a 
glutinous  covering  or  by  settling  among  the  particles  by  inter- 
position. 

Among  the  first  class  are  kerosene  oil,  petroleum,  sugar-cane 
juice,  molasses,  moss,  seaweeds,  potatoes,  tallow  and  starch. 


316  STEAM-BOILERS 

Kerosene  is  considered  better  than  petroleum,  and  both  act  well 
when  sulphates  are  present.  Most  of  the  other  substances  contain 
acetic  ac!d  and  act  best  when  the  sulphates  are  absent.  The 
acetic  acid  will  attack  the  boiler-plates  and  the  organic  compounds 
will  form  scale  with  any  sulphates  that  may  be  present. 

Among  the  second  class  are  clay  and  some  kinds  of  wood,  such 
as  mahogany,  logwood  and  hemlock  bark,  in  the  form  of  powder 
or  fine  chips,  which  may  be  introduced  with  the  feed.  The  sub- 
stance is  expected  to  settle  along  with  the  deposit  and  facilitate 
its  removal  by  preventing  a  solid-mass  formation.  These  sub- 
stances, however,  increase  the  solid  matter  in  the  boiler,  and  their 
distributed  settlement  throughout  the  mass  of  scaling  deposit 
cannot  be  relied  upon.  They  are,  therefore,  as  a  class  better 
avoided. 

Some  of  the  anti-incrustation  compounds  act  according  to 
one  or  both  of  the  above  methods.  In  general  they  should  be 
used  with  caution,  as  many  of  them  will  cost  the  steam-user 
more  in  the  reduced  life  of  the  boiler  than  they  save  in  coal. 

Fourth — Galvanic  Agents.  Sheets  of  zinc  have  been  used  in 
the  inside  of  boilers,  and  the  results  claimed  have  been  more  or 
less  favorable.  Their  use  is  principally  in  connection  with  salt 
water  and  their  efficacy  appears  to  be  due  to  the  action  of  the 
alkaline  chloride  of  zinc  on  the  salts  forming  the  scale. 

Fifth — Surface-condensing.  The  exhaust  steam  is  condensed 
in  a  surface  condenser,  and  the  hot  water  saved  and  pumped  back 
into  the  boiler,  fresh  water  only  being  used  to  supply  losses  from 
leaks,  safety-valve  and  whistle.  This  method  is  common  in  marine 
practice,  but  not  so  frequently  used  on  land  on  account  of  the 
scarcity  or  expense  of  water  for  condensing  or  cooling  purposes. 
Since  all  the  oil  and  grease  used  in  the  engine  cylinders  pass  into 
the  condenser,  it  is  necessary  to  filter  the  water  before  it  is  returned 
to  the  boiler.  This  is  done  by  some  filtering  material,  as  sponges, 
straw,  salt-meadow  hay,  excelsior,  flannel,  etc..  arranged  in  a 
variety  of  ways. 

If  insufficient  cooling  water  be  used,  the  elevation  of  tempera- 
ture will  cause  a  deposit  to  form  on  the  condenser  tubes,  especially 
when  much  bicarbonate  of  lime  is  present.  No  deposit  takes  place 
when  salt  water  is  used  for  cooling  purposes,  because  the  salt 
cannot  be  precipitated  by  elevation  of  temperature.  If,  however, 


INCRUSTATION  317 

the  condenser  leaks,  the  salt  water  would  enter  the  feed  and  deposit 
in  the  boiler. 

Sixth — Purification  by  Heating  and  Filtering  previous  to 
entrance  into  the  boiler.  It  is  now  becoming  quite  common  to 
heat  the  feed-water  when  bad  under  pressure  in  a  closed  vessel, 
warmed  by  exhaust  or  live  steam.  Under  this  treatment  the  lime, 
magnesia,  etc.,  are  nearly  all  deposited  in  this  external  collecting 
vessel,  which  should  be  so  arranged  as  to  be  easily  and  quickly 
cleaned. 

Feed-heating  coils  are  sometimes  arranged  in  the  smoke-flue, 
but  if  the  water  is  bad  this  method  should  not  be  encouraged,  as 
such  pipes  are  not  easy  to  get  at  unless  the  boiler  be  shut  down 
or  a  by-pass  smoke-flue  provided. 

It  is  evident  that  this  treatment  does  not  prevent  incrustation, 
but  merely  allows  the  deposit  to  form  in  a  special  vessel  separate 
from  the  boiler,  in  which  the  scale  is  not  liable  to  be  baked  hard. 

Many  of  the  anti-incrustation  compounds  might  be  used  in  one 
of  these  vessels  more  advantageously  than  in  the  boiler  itself, 
although  they  cannot  be  recommended  even  in  such  a  connection. 
These  external  vessels  form  a  feed-heating  apparatus,  since  the 
water  must  be  heated  to  a  high  degree  before  the  vessel  becomes 
effective  as  a  purifier. 

When  the  feed  contains  large  quantities  of  matter  in  suspension, 
it  is  well  to  filter  it  through  sand,  pebbles,  etc.,  before  pumping 
it  into  the  boiler.  Such  filters  should  be  arranged  to  be  easily 
cleaned,  which  is  generally  done  by  passing  the  wash  water  through 
it  in  a  reverse  direction  and  allowing  it  to  waste. 

Seventh — Internal  Collecting  Apparatus.  Sometimes  curved 
plates  and  troughs  of  various  shapes  are  arranged  inside  of  the 
boiler  with  some  success.  It  is  intended  that  the  major  part  of 
the  deposit  will  form  on  these  surfaces,  which  should  be  made  to 
be  easily  removed,  cleaned  and  replaced. 

Thus  the  feed  can  be  arranged  to  discharge  into  a  trough  placed 
just  above  the  water-line,  and  in  which  the  water  will  be  compara- 
tively quiet  and  free  from  ebullition.  The  surplus  feed  will  over- 
flow the  edges.  Most  of  the  lime  and  magnesia  salts  will  deposit 
in  the  trough  on  account  of  the  increase  of  temperature.  Such 
an  arrangement  works  best  with  the  sulphates  and  heavy  deposits. 

Internal-collecting     apparatus    when    complicated    interferes 


318  STEAM-BOILERS 

with  the  proper  inspection  and  cleaning  of  the  boiler  itself,  and 
it  is  better  to  have  the  collecting  device  outside  of  the  boiler,  in  a 
feed  purifier  of  good  design,  as  described  under  the  sixth  treatment. 

Eighth — Removal  by  Manual  Labor.  In  erecting  a  new  plant 
where  bad  water  only  is  available,  the  greatest  care  should 
be  taken  to  select  a  boiler  that  has  a  strong  circulation  over  crown 
sheets  and  parts  subjected  to  great  heat  and  difficult  to  clean. 
Patented  devices  to  attach  to  boilers  to  strengthen  their  circulation 
are  not  always  reliable. 

After  the  incrustation  has  formed  to  a  certain  thickness,  de- 
pending on  local  circumstances,  the  boiler  is  blown  off  and  the  scale 
detached  and  removed  by  manual  labor.  This  chipping  of  the  scale 
is  often  a  difficult  work;  and  when  it  is  hard,  the  men,  if  careless, 
are  apt  to  injure  the  surface  of  the  plates  and  the  ends  of  the  rivets. 
Dents  or  abrasions  thus  formed  in  the  surface  of  the  metal  afford 
good  opportunity  for  the  corrosive  action  of  the  feed-water. 

Special  tools  often  are  made  to  conveniently  reach  difficult 
places;  and  chains  are  sometimes  inserted  in  the  water-legs,  so  as 
to  wear  off  the  scale  by  attrition,  as  they  are  drawn  back  and  forth. 

When  a  boiler  is  suddenly  blown  off  while  hot  and  then  refilled 
with  cold  water,  the  scale  is  frequently  cracked  and  loosened,  and 
perhaps  thrown  down  by  the  contraction  of  the  plates.  This  is, 
however,  a  very  injurious  process,  and  should  never  be  permitted. 
It  simply  saves  the  cost  of  a  little  manual  labor. 

On  the  other  hand,  if  the  boiler  be  allowed  to  cool  gradually, 
and  then  be  blown  off  after  standing  full  of  water  for  three  or  four 
days,  the  deposits  are  not  apt  to  be  baked  hard,  and  some  of  the 
salts  may  be  softened  or  redissolved.  The  objection  to  this  latter 
treatment  is  the  long  time  the  boiler  is  out  of  service,  but  as  all 
important  plants  should  have  a  spare  boiler,  this  objection  has 
less  practical  value  than  would  at  first  appear. 

If,  however,  time  is  an  important  feature,  the  cooling  of  the 
boiler  may  be  hastened  by  pumping  in  fresh  water  as  the  hot  is 
slowly  blown  out.  This  treatment,  when  done  slowly,  will  uni- 
formly cool  off  the  boiler,  and  will  also  keep  the  bottom  blow  from 
becoming  clogged  or  choked  with  sludge,  as  may  happen  if  the 
boiler  be  allowed  to  stand  for  some  time. 


CHAPTER    XIII 
CORROSION.  GENERAL  WEAR  AND  TEAR.  EXPLOSIONS 

Corrosion.  Wasting.  Pitting  and  Honey-combing.  Grooving.  Influ- 
ence of  Air  and  Acidity.  Galvanic  Action.  Zinc  Plates.  External  Corro- 
sion. Dampness.  Wear  and  Tear.  Idle  Boilers.  Explosions.  Stored 
Energy. 

FROM  the  moment  the  boiler  is  finished,  it  gradually  becomes 
weaker,  due  to  the  destroying  forces  that  are  continually  acting 
upon  it.  These  forces  are  of  both  a  chemical  and  a  mechanical 
nature,  and  keep  up  their  influences  with  an  ever-increasing 
rapidity. 

Corrosion,  which  takes  place  both  internally  and  externally, 
is  the  most  serious  and  subtle  cause  of  weakening  to  which  a  boiler 
is  subjected. 

Internal  corrosion  is  generally  in  the  form  of  uniform  wasting, 
of  pitting  and  of  grooving. 

This  Wasting  Away  of  the  plates  is  seldom  so  uniform  in  its 
effects  as  rusting,  but  it  usually  covers  large  patches  of  surface. 
It  is  produced  by  some  chemical  action  of  the  water  on  the  plates. 
It  is  more  or  less  easy  of  detection.  Sometimes  it  produces 
"  bleeding,"  that  is,  the  scale  and  plates  in  the  vicinity  are  streaked 
with  red.  When  wasting  is  very  extended,  it  is  apt  to  pass  un- 
noticed on  a  hasty  examination,  but  it  is  always  revealed  by  drilling 
the  plate  and  calipering.  This  precaution  of  drilling  should 
always  be  resorted  to  with  old  boilers.  There  are  no  rules  to  guide 
the  inspector  in  searching  for  wasting,  and  it  does  not  appear  to 
take  place  in  two  boilers  alike.  However,  the  water-line  appears 
to  be  especially  liable  to  attack  in  boilers  that  stand  quiet  for  a  long 
time.  For  this  reason  boilers  should  not  be  allowed  to  stand  idle 
when  only  partly  filled  with  water.  Sometimes  this  corrosion  is 

319 


320  STEAM-BOILERS 

hidden  under  a  thin  shell  or  crust  of  metal,  when  its  presence  can 
be  detected  by  a  testing  hammer. 

Pitting,  or  honey-combing,  is  in  general  well  defined.  It  con- 
sists of  small  depressions  of  varying  shapes  and  forms.  When  the 
depressions  are  extended  the  effect  is  more  like  wasting.  It  is 
not  limited  to  any  parts  of  the  boiler,  and  it  often  appears  in  the 
steam  space.  The  depressions  are  sometimes  filled  with  a  fine 
powder,  being  a  mixture  of  iron,  silica  and  other  earthy  matters, 
and  a  small  percentage  of  oil.  The  depressions  are  occasionally 
covered  with  a  hard  crust  like  a  blister,  but  more  frequently  are 
open  with  sharp  edges. 

M.  Olroy,  a  French  engineer,  thus  states  *  the  results  of  his  in- 
vestigations of  the  pitting  of  boilers:  " Pitting  is  particularly  likely 
to  occur  if  a  water  very  free  from  lime  is  used  in  clean  boilers. 
When  a  boiler  forms  one  of  a  battery  and  is  kept  standing  for  a 
long  interval,  the  top  of  the  boiler  is  liable  to  pitting.  Steam 
finds  its  way  into  the  boiler,  and  condensing  upon  the  top  surface, 
causes  bad  pitting  there.  Pure  water  containing  no  air  does 
not  harm,  and  steam  alone  will  cause  no  pitting  unless  it  contains 
a  supply  of  air.  The  Loch  Katrine  water  of  Glasgow,  which  causes 
pitting  in  clean  boilers,  contains  much  gas.  The  water  from 
many  of  the  lakes  in  America  also  produces  the  same  effect.  With 
distilled  water  the  boilers  usually  remain  quite  bright.  Feed- 
water  heaters  often  suffer  badly  from  pitting,  particularly  near  the 
cold-water  inlet,  and  in  boilers  the  parts  most  likely  to  be  attacked 
are  those  where  the  circulation  is  bad,  especially  if  such  portions 
are  also  near  the  feed  inlet. 

"In  locomotives  the  bottom  of  the  barrel  and  the  largest  ring 
is  most  frequently  attacked.  The  steam  spaces  are  generally  free 
from  pitting,  unless  the  boiler  is  frequently  kept  standing  with 
water  in  it.  As  the  water  evaporates  or  leaks  away,  pitting  is 
liable  to  occur  along  the  region  of  the  water-line,  a  part  which 
in  a  working  boiler  is  generally  free  from  attack,  unless  the  longi- 
tudinal seam  is  near  that  point  and  forms  a  ledge  where  the  moisture 
can  rest. 

"Pittings  take  the  form  of  cones  or  spherical  depressions,  which 
are  filled  with  a  yellowish-brown  deposit  consisting  mainly  of  iron 
oxide.  The  volume  of  powder  is  greater  than  that  of  the  metal 

*  Engineering,  19  October,  1894,  Vol.  LVII. 


CORROSION  321 

oxidized,  so  that  a  blister  is  formed  above  the  pit  which  has  a 
skin  as  thin  as  an  egg-shell.  This  skin  usually  contains  both  iron 
oxide  and  lime  salts  and  differs  greatly  in  toughness.  In  many 
cases  it  is  so  friable  that  it  breaks  at  the  least  shock,  falling  to 
powder,  while  in  other  cases  the  blister  detaches  itself  from  the 
plate  as  a  whole. 

"An  analysis  of  the  powder  in  the  pits  shows  it  to  consist  of 
peroxide  of  iron,  86.26  per  cent;  grease  and  other  organic  matter, 
6.29  per  cent;  lime  salts,  4.25  per  cent;  water,  silica,  aluminum, 
etc.,  3.20  per  cent.  The  skin  over  the  pits  was  found  to  contain 
calcium  carbonate,  38  per  cent;  calcium  sulphate,  12.8  per  cent: 
and  iron  oxide,  FeO,  32.2  per  cent,  and  about  8.5  per  cent  each 
of  magnesium  carbonate  and  insoluble  matter." 

Grooving  occurs  along  the  edges  of  laps,  angle-bars,  stays 
and  doubling-plates.  It  is  caused  primarily  by  too  great  a  stiff- 
ness, resisting  the  expansion  and  contraction.  This  stiffness  com- 
pels the  play  or  breathing  of  the  boiler  to  take  place  locally,  simi- 
larly to  bending  back  and  forth  a  thin  plate  with  the  hands.  It 
is  sometimes  initiated  through  injury  to  the  plates  by  a  careless  use 
of  the  calking  chisel  or  cleaning  tool.  In  a  crack  once  started, 
grooving  increases  rapidly,  due  to  the  corrosive  action  entering 
deeply  into  the  plate  and  exposing  fresh  surfaces. 

When  cylindrical  boiler-shells  are  too  firmly  seated  on  their 
foundations,  the  expansion  may  promote  grooving  by  causing 
the  plate  to  buckle  near  the  lap  and  butt-straps,  especially  those  of 
the  transverse  or  ring  seams.  If  the  shell  be  not  perfectly  cylin- 
drical, it  tends  to  become  so  under  pressure,  and  the  longitudinal 
seams  are  similarly  affected. 

Grooving  may  also  be  caused  by  lack  of  stiffness.  For  instance, 
in  vertical  fire-box  boilers,  grooving  is  liable  to  occur  at  the  mud- 
ring  when  this  ring  is  not  made  of  sufficient  depth  to  resist  the 
upsetting  action  caused  by  the  expansion  of  the  fire-box  sheet 
being  greater  than  that  of  the  outer  shell  sheet. 

To  prevent  grooving  of  the  head  or  end  plates  at  the  flange 
or  angle  where  they  join  the  shell,  tubes,  flues  and  stays  should 
not  be  located  too  near  the  shell;  the  flange  should  be  turned 
with  an  easy  radius,  about  two  and  a  half  thicknesses,  and  the 
head  should  be  made  as  thin  as  safety  will  permit. 

Internal  corrosion  appears  to  be  caused  by  acidity  and  air  in 


322  STEAM-BOILERS 

the  feed  water,  and  perhaps  in  special  cases  to  some  form  of  gal- 
vanic action.  Such  galvanic  action  has  been  counteracted  by 
the  use  of  zinc  plates.  The  electric  couple  separates  the  hydrogen, 
which  passes  to  the  steel  and  then  escapes  into  the  steam  space, 
while  the  oxygen  goes  to  the  zinc.  The  proportions  found  requisite 
to  insure  protection  are  about  1  square  foot  of  zinc  to  50  square 
feet  of  heating  surface  in  new  boilers,  and  the  same  quantity  of 
zinc  to  75  or  100  square  feet  of  surface  in  older  boilers.  The  zinc 
plates  should  be  about  10  inches  by  6  inches  by  ^-inch  thick.  The 
contact  between  the  zinc  and  steel  must  be  a  good  metallic  con- 
tact in  order  to  be  effective.  Usually  the  zinc  is  bolted  to  con- 
venient stays  or  to  studs  formed  for  the  purpose  on  the  combustion- 
chamber.  The  contact  surfaces  should  be  bright  and  clean,  and 
the  nuts  should  be  well  screwed  down  to  prevent  scale  forming  be- 
tween them.  Zinc  slabs  will  last  from  two  to  three  months. 
The  zinc  is  often  carried  in  metal  baskets  to  catch  pieces  that 
break  off  from  time  to  time. 

The  varied  appearance  and  location  of  corrosion  may  be  caused 
by  the  lack  of  either  physical  or  chemical  homogeneity  in  the 
metal.  In  order  to  prevent  internal  corrosion,  the  causes  should 
be  studied  and  neutralized  as  far  as  possible.  The  materials  of 
the  boiler  should  be  as  homogeneous  as  possible;  the  feed- water 
should  be  kept  slightly  alkaline  by  the  use  of  soda  and  be  free  from 
air.  A  thin  coating  of  scale  will  often  act  as  a  protective  covering. 
When  corrosion  has  attacked  a  surface  that  is  not  directly  exposed 
to  the  fire  or  hot  gases,  it  will  often  be  found  beneficial  to  clean 
the  spot  and  wash  it  well  with  soda,  and  paint  it  with  a  thin  layer 
of  Portland  cement.  Wherever  boilers  are  liable  to  excessive  cor- 
rosion, they  should  be  most  carefully  examined  at  regular  inter- 
vals. This  is  true  for  external  as  well  as  internal  corrosion. 

External  Corrosion  is  just  as  active  as  internal  corrosion,  and 
in  many  ways  is  more  dangerous,  since  it  is  not  so  often  sus- 
pected and  since  boilers  are  frequently  so  set  as  to  be  difficult  to 
properly  inspect. 

The  forms  are  similar  to  those  of  internal  corrosion.  It  is 
generally  produced  by  leaks  or  dampness,  and  the  drippings  from 
fittings  and  gauges.  Ashes  will  rapidly  corrode  any  metal  against 
which  they  lie. 

A  brick  setting  should  be  kept  away  from  contact  with  the 


GENERAL  WEAR  AND  TEAR  323 

shell,  and  care  should  be  exercised  not  to  cover  a  longitudinal 
seam.  In  fact  all  seams  should  be  exposed,  as  far  as  the  design 
will  permit,  that  leaks  may  be  detected  at  once.  The  brick 
setting  should  be  carried  to  within  about  f-inch  of  the  shell,  and 
this  space  be  packed  with  fire-clay  or  asbestos  fibre.  Many  boilers 
are  so  set  that  their  tops  are  covered  with  a  brick  arch.  It  would 
be  better,  when  possible,  to  construct  the  side  and  back  walls  high 
enough  to  retain  a  heavy  layer  of  clean  dry  sand.  This  sand  can 
always  be  pushed  aside  for  the  purpose  of  inspection.  When 
felting,  asbestos,  magnesia  or  similar  coverings  are  used,  they 
should  be  laid  so  as  to  touch  the  boiler  without  an  air  space,  that 
any  leak  may  soak  through  and  become  visible.  All  fittings  or 
attachments  covered  by  brickwork,  such  as  blow-off  connections, 
should  be  avoided,  as  they  cannot  be'  inspected  except  by  the 
removal  of  the  masonry. 

General  Wear  and  Tear  weakens  a  boiler  by  a  more  or  less 
gradual  process,  with  activity  increasing  with  age  and  lack  of 
care.  Repeated  expansion  and  contraction,  especially  when 
sudden  and  local,  are  principal  factors  of  encouragement.  When 
boilers  are  fired  up  too  suddenly,  certain  parts  are  heated  faster 
than  others,  and  undue  stresses  are  brought  to  bear  which  often 
cause  buckling  and  straining.  This  effect  is  noticed  on  the  trans- 
verse or  ring  seams,  which  show  a  tendency  to  groove  under  the 
laps  or  butt-straps.  Length  of  shell,  therefore,  may  be  an  element 
of  weakness,  although  the  metallic  strength  to  resist  bursting  has 
been  shown  to  be  independent  of  length. 

Boilers  often  leak  after  having  been  tested  and  made  tight. 
This  may  be  due  to  a  variety  of  causes,  but  usually  can  be  traced 
to  severe  handling  or  to  excessive  variations  in  temperature. 
Sometimes  the  cold  feed  enters  so  as  to  impinge  against  a  hot 
plate,^tube  or  riveted  seam,  and  leakage  is  sure  to  result.  Leaky 
rivets  should  not  be  calked  too  much.  It  is  better  to  cut  out  the 
rivet  in  fault,  ream  the  hole  fair  and  insert  a  new  rivet  to  fit  the  new 
hole. 

Idle  Boilers  should  receive  attention.  When  boilers  are 
laid  off,  care  must  be  taken  to  arrest  the  actions  described  in  this 
chapter. 

The  outside  should  be  cleaned  and  painted  with  a  good  metallic 
paint,  applied  directly  to  the  cleaned  and  dried  surface.  If  the 


324  STEAM-BOILERS 

boiler  be  covered  by  lagging,  the  lagging  should  not  be  allowed 
to  absorb  moisture  from  the  atmosphere. 

On  the  fire  side,  the  soot  and  ashes  should  be  thoroughly 
removed  and  the  surface  cleaned.  These  surfaces  should  then 
be  kept  dry  and  not  exposed  to  damp  air  Fresh  lime  in  pans  or 
trays,  renewed  as  required,  will  absorb  the  moisture  in  the  air 
Occasional  small  fires  of  tarred  wood  will  be  beneficial,  as  the  heat 
will  dry  the  metallic  surfaces  and  the  resinous  condensations  fiom 
the  thick  smoke  will  cover  the  tubes  and  shell  with  a  protective 
coating. 

On  the  water  side,  corrosion  may  be  active  at  the  water-line 
if  the  boiler  be  left  partly  full.  Idle  boilers  should,  therefore,  be 
entirely  dry  or  completely  filled  with  water.  If  the  laying  off 
is  for  a  short  time  only,  it  is  a  good  plan  to  fill  the  boiler  with  water 
made  alkaline  by  a  little  soda.  If  for  a  long  period,  it  seems  best 
to  empty  the  boiler  and  dry  out  the  inside  by  a  small  fire  built  in 
a  pan,  which  can  be  inserted  through  the  lowest  manhole.  The 
manhole  and  handhole  covers  can  be  put  back  and  the  boiler 
made  tight  so  that  the  oxygen  will  be  consumed  by  the  fire,  or  the 
covers  can  be  left  off  and  lime  in  trays  used  to  absorb  any  moisture. 

Explosions  occur  when  the  steam  pressure  exceeds  the  resisting 
strength  of  the  metal  structure. 

In  a  well-designed  boiler  the  parts  are  of  approximate  equal 
strength  throughout.  It  is  good  practice  to  so  design  a  boiler 
that  those  parts  shall  have  an  excess  of  strength  which  are  ex- 
pected to  suffer  most  rapidly  from  corrosion  or  wear  and  tear. 
Then  as  the  boiler  advances  in  age,  the  various  parts  become  more 
nearly  equal  in  strength. 

Should  a  boiler  become  weakened  and  a  rent  occur,  the  steam 
pressure  will  be  suddenly  reduced,  thus  releasing  the  heat  stored 
in  the  water.  The  water  instantly  flashing  into  vapor  probably 
accounts  for  the  great  destructive  effects  produced  by  an  explosion. 

While  the  rent  primarily  occurs  at  some  weak  spot,  the  fracture 
may  not  and  seldom  does  follow  a  line  of  structural  weakness. 
The  new  forces  set  up  at  the  instant  of  explosion  no  doubt  account 
for  this  phenomenon. 

Imagine  a  boiler  to  contain  60  cubic  feet  of  water  and  10  cubic 
feet  of  steam  under  a  pressure  of  120  pounds  per  square  inch  above 
the  atmosphere.  Since  each  cubic  foot  of  water  weighs  57.3  pounds 


EXPLOSIONS  325 

and  each  cubic  foot  of  steam  0.301  pound,  the  total  heat  contained 
above  212°  F.  in  B.  T.  U.  would  be: 

60X57.3X  (321.4- 180.7)  =  483,726 
10  X  0.301  X  (1106. 1-1074.2)=          96 

483,822   B.T.  U. 

and  483,822  X  778  =  376,413,516  foot-pounds. 

Consider  the  problem  in  another  way.  The  work  could  be  ex- 
pressed by  the  change  of  volume  of  the  water  into  steam  times  the 
atmospheric  pressure  plus  the  expansion  of  the  steam  to  atmos- 
pheric pressure,  or 

3.323X  144X  14.7X60X  57.3  =  24,183,291 
PiV1  hyp-log  r 

2fi  fi4 
=  144X135X3.323  hyp-log  -^X  60X57.3  =  462,284,027 

o  .0—0 

Work  in  foot-pounds  =  486,467,228 

Neither  of  these  assumptions  correctly  measures  the  power  ex- 
pended, but  as  exact  data  are  always  missing  at  time  of  explosion, 
no  accurate  calculation  can  be  made.  The  figures  illustrate  two 
facts :  first,  that  there  is  sufficient  energy  in  the  boiler  to  create 
the  destru3tive  effects  attributable  to  an  explosion;  and,  second, 
that  the  energy  stored  in  the  steam  is  very  much  less  than  in  the 
hot  water.  All  things  being  equal,  the  damaging  effect  by  explosion 
of  water-tubular  boilers  will  be  less  than  of  fire-tubular  boilers  of 
equal  rating,  since  the  former  contain  a  smaller  proportion  of  water, 
and  since  extra  time  will  be  required  for  complete  release,  because 
the  bursting  part  is  small. 

Failures  of  boilers  are  usually  due  to  wear  and  tear,  produced 
chiefly  by  expansion  and  contraction,  to  corrosion,  to  overheating 
and  to  carelessness.  Overheating  may  be  caused  by  low  water 
or  by  scale  or  grease.  Important  fixtures,  such  as  main  stop- 
valves,  may  become  attacked,  or  the  main  steam-pipe  may  be 
burst  by  water-hammer,  thus  causing  a  sudden  release  of  pressure, 
which,  if  quick  enough,  may  be  followed  by  an  explosion. 

Explosions  of  sectional  boilers  of  the  water-tubular  type  do 
not  produce  effects  so  destructive  as  those  created  by  fire-tubular 
boilers.  Most  water-tubular  boilers  could  blow  out  a  tube  and  still 


326  STEAM-BOILERS 

not  explode,  as  the  time  required  to  release  the  pressure  is  an  all- 
important  element.  This  property  is  one  of  the  chief  claims 
favorable  to  that  class. 

When  an  explosion  does  occur,  it  is  frequently  very  difficult  to 
determine  the  cause,  and  hasty  judgment  should  always  be  with- 
held. A  good  piece  of  metal  may  show  a  poor  quality  of  fracture 
on  account  of  the  suddenness  of  the  rupture.  Opinion  as  to  the 
quality  of  the  metal  should  only  be  given  after  a  close  and  careful 
analysis  of  physical  and  chemical  tests. 

The  best  way  to  prevent  explosion  is  to  employ  intelligent  labor 
and  not  neglect  proper  and  regular  inspection. 


CHAPTER    XIV 
CHIMNEY    DESIGN 

Object.  Selection  of  Height.  Compare  Cost  of  Stack  with  Mechan- 
ical Draft.  Individual  Stacks  in  Lieu  of  One  Large  Stack.  Self-supporting 
and  Non-self-supporting  Stacks.  Wind  Pressure.  Batter.  Brick  Stacks. 
Section.  Lining.  Top.  Lightning.  Ladder.  Leakage.  Steel  Stacks. 

A  chimney  or  stack  is  a  necessary  adjunct  to  all  furnaces. 
It  has  a  twofold  use,  namely,  to  create  a  draft  or  current  of  air 
through  the  bed  of  fuel,  so  that  the  process  of  combustion  may 
be  continuous;  and  to  discharge  the  products  of  combustion  at 
such  elevations  as  to  be  least  objectionable. 

When  the  design  relies  upon  natural  draft,  the  stack  must  have 
the  requisite  area  of  flue  and  height  to  produce  the  flow  of  hot  gases 
through  it,  as  determined  by  the  quantity  of  fuel  to  be  burned  in 
a  given  time.  Owing  to  the  ever-changing  conditions,  as  tempera- 
tures of  air  and  gases,  grade  of  fuel,  rate  of  combustion  to  suit 
variations  of  work,  etc.,  the  height  is  usually  settled  by  experience. 
If  there  is  doubt,  give  preference  to  increase  of  height,  as  too  strong 
a  draft  is  rather  a  good  fault  than  otherwise.  If  on  account  of 
the  cost,  or  for  any  other  reason,  the  desired  height  cannot  be 
secured,  then  the  flue  area  should  be  made  proportionately  larger, 
so  that  the  required  quantity  of  gases  can  be  discharged  at  a  lower 
velocity. 

With  a  mechanical  draft,  the  height  of  stack  need  only  be  such 
as  to  obtain  a  suitable  outlet  for  the  gases. 

Where  the  products  must  be  discharged  so  as  not  to  create  a 
nuisance,  no  fixed  information  as  regards  height  is  available,  but 
each  case  must  be  worked  out  from  its  peculiar  surrounding  con- 
ditions. 

A  good,  strong,  natural  draft  is  most  desirable,  since  it  pro- 
duces an  even  and  economical  combustion  of  coal.  Its  intensity 

327 


328  STEAM-BOILERS 

is  controllable  to  suit  varying  conditions  by  the  use  of  the  damper. 
But  to  obtain  a  strong,  natural  draft  capable  of  drawing  the 
products  of  combustion  through  the  furnace  and  boiler,  as  well  as 
through  a  feed-water  heater  or  economizer,  means  the  construction 
of  a  high  stack.  The  cost  of  producing  this  draft  is  evidently  the 
sum  of  the  repair,  interest  and  depreciation  charges  against  the 
stack.  If  the  stack  is  very  high  and  of  expensive  construction, 
natural  draft  is  costly. 

Before  the  final  design  of  the  stack  is  determined,  the  cost  of  an 
equivalent  draft  produced  by  mechanical  means  should  be  con- 
sidered for  comparison.  A  mechanical  draft  might  save  sufficient 
in  first  cost  of  stack,  that  the  interest  on  this  amount  added  to  the 
repairs  of  the  proposed  stack  may  pay  the  charges  for  operation, 
maintenance  and  depreciation  on  the  mechanical-draft  apparatus. 

Owing  to  the  great  cost  of  tall  stacks,  many  plants  are  providing 
a  number  of  short  stacks  the  aggregate  cost  of  which  would  be 
less.  Furthermore,  when  a  number  of  boilers  are  connected  to 
one  stack,  some  are  liable  to  rob  others  of  draft,  a  state  of  affairs 
difficult  to  prevent  in  practical  operation.  This  can  be  obviated 
by  separate  stacks  to  each  boiler  or  by  one  stack  common  to  three 
boilers  when  such  boilers  are  set  close  together.  The  separate 
stack  plan  does  away  with  a  long  breeching  or  flue  connection  to 
the  stack,  which  is  often  an  item  worthy  of  consideration,  both  as 
to  cost  and  loss  of  draft  "head."  The  breeching  being  horizontal  or 
nearly  so,  permits  of  accumulations  of  soot,  which  may  cause  cor- 
rosion and  presents  difficulties  to  clean  unless  all  the  connecting 
boilers  be  shut  down. 

Stacks  may  be  of  two  kinds,  self-supporting  and  non-self- 
supporting.  The  latter  class  requires  bracing  against  side  pres- 
sures due  to  wind.  Such  braces  or  guys  are  generally  of  wire  rope 
f -inch  in  diameter,  or  iron  rods  4-inch  in  diameter  and  10  to  20  feet 
long,  linked  together  like  a  chain. 

The  weight  of  the  stack  is  carried  by  the  foundation,  which 
must  have  an  area  determined  according  to  the  bearing  properties 
of  the  soil.  The  weight  to  be  supported  is  the  dead  weight  of  the 
structure  plus  the  wind  load.  The  area  or  strength  of  the  stack 
at  any  point  must  be  capable  of  carrying  the  weight  and  wind 
stresses  above  such  a  point. 

The  wind  acts  as  an  overturning  force  and  is  resisted  by  gravity. 
Stability  calculations  should  be  made  at  frequent  sections.  For 


CHIMNEY  DESIGN  329 

a  masonry  stack,  the  resultant  of  the  wind  and  weight  forces  should 
pass  through  the  section  considered  not  farther  from  the  axis  than 
the  sum  of  one-half  the  outer  radius  plus  one-quarter  the  inner  ra- 
dius. If  the  stack  be  square  or  octagonal,  use  the  radii  of  the  in- 
scribed circles.  Calculations  should  be  made  for  compression  and 
tension.  The  maximum  compression  for  radial  brick  is  taken 
generally  at  15  tons  per  square  foot,  and  the  tension  at  2J  tons. 
The  formula  is: 

Weight       Wind  moment 

.      — ±o — --. r— : — =  Max.  unit  stress. 

Area       Section  modulus 

In  estimating  the  weight,  only  that  of  the  stack  and  base 
should  be  considered.  The  weight  of  the  lining  should  be  omitted 
unless  of  a  very  permanent  character. 

To  increase  the  stability,  the  sides  of  base  can  be  lengthened  by 
making  the  foundation  on  a  vertical  batter  of  one  horizontal  to 
three  vertical. 

It  is  customary  to  assume  the  wind  pressure  at  50  pounds  per 
square  foot  of  surface  and  as  acting  on  the  full  vertical  area  of  one 
side  of  square  stacks,  on  three-fourths  the  area  of  vertical  section 
of  octagonal  stacks,  and  on  one-half  the  area  of  vertical  section  of 
round  stacks.  The  point  of  application  of  the  pressure  is  taken  at 
the  centre  of  area  of  the  exposed  section.  It  is  highly  probable  that 
the  centre  of  pressure  is  above  that  point  due  to  the  lesser  velocity 
of  wind  at  points  low  down,  since  the  air  is  appreciably  retarded  by 
friction  with  the  ground.  Ample  allowance  should,  therefore,  be 
provided  by  assuming  a  high  wind  velocity. 

Excepting  short  steel  stacks  that  are  bolted  directly  to  the 
boiler,  the  bases  should  be  made  to  spread  out  in  order  to  add  to 
the  stability.  Stacks  should  taper  toward  the  top  with  a  batter 
of  not  less  than  T1g-inch  to  the  foot  when  of  brick,  while  steel 
stacks  may  have  a  smaller  batter  if  desired.  Short  steel  stacks 
are  usually  made  parallel.  If  there  is  too  small  a  batter,  tall  stacks 
will  look  top-heavy,  and  the  required  amount  of  batter  largely 
depends  on  appearance. 

Stacks  are  made  of  brick,  reinforced  concrete,  and  steel,  and 
the  foundations  are  either  of  brick,  stone,  or  concrete.  In  pre- 
paring a  design  it  will  be  found  just  as  simple  and  cheap  to 
make  the  stack  graceful  and  pleasing  to  the  eye  as  to  create  an 
ugly  and  stiff  looking  structure.  All  fancy  ornamentation  or 


330  STEAM-BOILERS 

pattern  work  should  be  avoided  as  being  unsuitable  and  detract- 
ing from  the  general  appearance  of  solidity.  Any  ornamentation 
of  a  kind  that  will  rapidly  deteriorate  should  especially  be  omitted. 
A  plain,  simple  design  having  easy  and  graceful  lines  is  the  one 
most  appreciated.  A  study  of  the  designs  of  chimneys  as  pub- 
lished in  the  engineering  periodicals  will  well  repay  the  trouble 
before  completing  a  new  design. 

Brick  Stacks.  The  round  section  is  the  most  effective,  but 
it  is  also  the  most  costly.  Next  to  it  is  the  octagonal  section,  and 
then  the  square. 

The  round  chimney  is  generally  difficult  to  locate  close  to  build- 
ings without  causing  a  waste  of  room.  The  base,  however,  can  be 
made  square,  giving  the  appearance  of  a  pedestal  to  the  cylindrical 
shaft  which  is  often  pleasing.  Round  flues  are  theoretically  pref- 
erable to  square  ones  as  offering  less  frictional  surface,  but  in 
stacks  of  moderate  height  there  appears  to  be  little,  if  any,  prac- 
tical difference  in  the  draft  intensity.  For  tall  stacks  the  round 
section  is  to  be  preferred,  and  is  favored  by  many  engineers  for 
all  cases.  Under  ordinary  conditions,  structural  and  esthetic  con- 
siderations should  settle  the  flue  section  and  consequently  the 
outside  section  to  be  adopted. 

The  structure  should  be  built  with  good,  sound  bricks  of  uni- 
form color,  laid  flush  in  cement  mortar,*  having  a  minimum  thick- 
ness at  top  of  8^  inches  for  common  brick  and  7  inches  for  radial 
brick.  It  should  be  lined  with  fire-brick,  the  lining  being  carried 
up  from  half  to  two-thirds  the  height  in  short  stacks  and  from  one- 
quarter  to  one-third  in  tall  ones.  The  lining  should  be  independ- 
ent of  the  stack,  leaving  a  space  at  the  bottom  tapering  to  nothing 
at  the  top,  so  that  it  may  expand  freely  and  be  easy  to  remove  and 
renew.  The  header  bricks  of  the  lining  should  project  so  as  to 
touch  the  outer  wall,  but  not  be  bonded  to  it.  The  lining  may  be 
continued  up  with  hard-burnt  brick  after  the  fire-brick  stops,  if 
desirable.  Offsets  in  the  lining  to  increase  its  thickness  should 
be  made  on  the  outside,  and  sections  of  the  same  thickness  are 
generally  from  40  feet  to  50  feet  high.  The  top  section  is  usually 
about  4  inches  thick,  but  a  4-inch  section  should  not  be  over  25 

*  The  cement  may  be  a  mixture  of  Portland  cement,  slacked  lime  and 
sand,  in  the  proportions  of  1  measure  of  cement,  £  measure  of  lime  and  3 
measures  of  sand.  The  lime  is  added  to  make  the  mortar  set  slower  and 
work  smoother. 


CHIMNEY  DESIGNS 


331 


SECTION.B-B 


III 


)N  A-A 

FIG.  148.— Brick  Stack.    De- 
signed by  E.  S.  Farwell. 


feet  high.  The  flue  area  is  generally 
made  tapering  toward  the  top,  but 
sometimes  is  of  uniform  area. 

The  top  of  the  stack  should  be  fin- 
ished off  with  a  capital  of  suitable  de- 
sign. It  is  claimed  that  the  draft  may 
be  assisted  by  adopting  an  appropriate 
shape.  The  principle  of  the  claim  is  that 
the  upper  surface  should  incline  upward 
and  inward,  so  that  the  air  current  pass- 
ing over  the  chimney  will  cause  a  suc- 
tion. The  top  may  be  capped  with  stone 
flagging  or  by  an  iron  casting  shaped  to 
bond  the  last  courses  of  brick.  These 
iron  caps,  especially  when  large,  are 
best  made  in  sections  bolted  together 
through  flanges. 

Tall  stacks  are  protected  by  lightning- 
rods.  One  point  of  }-in.  solid  copper, 
sharpened  arid  tipped  with  platinum  cap 
1J  in.  long,  should  be  used  for  every  75 
feet  in  height.  The  points  are  connected 
to  a  stout  copper  band.  The  band  is  con- 
nected to  the  ground  by  two  conductors  of 
J-in.  stranded  copper  cable,  terminating 
in  a  coil  buried  at  least  6  feet  in  a  bed  of 
charcoal.  The  cables  should  be  secured 
to  the  stack  by  suitable  brass  anchors. 

There  should  be  a  ladder  on  every 
chimney,  made  of  iron  rods  about  |-inch 
in  diameter,  built  into  the  brickwork  at 
convenient  distances  apart,  generally 
about  every  16  inches.  The  ladder  may 
be  on  the  inside  or  outside  to  suit  the 
conditions  or  fancy  of  the  designer.  In 
general,  it  is  the  more  useful  when  on  the 
outside. 

The  connecting  flue  or  breeching  may 
enter  the  stack  through  the  side  or 


332 


STEAM-BOILERS 


through  the  base.  As  the  former  method  weakens  the  structure, 
the  latter  method  is  preferable  for  tall  stacks.  There  should  be 
an  entrance  manhole  or  door  to  clean  out  the  accumulations  of 
soot  from  the  base  of  the  flue. 

Brick  stacks  leak  large  quantities  of  air,  even  when  well  con- 
structed, which  naturally  tends  to  interfere  with  the  draft.  For 
this  reason  the  modern  tendency  favors  stacks  of  steel  wherever 
possible. 

The  cost  of  brick  stacks  cannot  be  estimated  by  the  cubic 
yards  of  masonry  contained,  as  so  much  depends  on  location, 
height  and  difficulty  of  constructing  a  scaffold. 

Steel  Stacks.  The  steel  plates  are  lapped  and  riveted,  rather 
than  butt- jointed  and  strapped,  as  the  lapped  seams  give  stiffness 


INCH  ROUND 


FIG.  149. — Ladder  for  Brick  Stack,  large  enough  for  a  man  to  climb  up 
inside  of  rungs. 

and  strength  and  are  cheaper.     Occasionally  the  plating  is  made 
flush  for  appearance,  especially  in  marine  work. 

Steel  stacks  that  are  not  self-supporting  should  have  guys 
fastened  at  proper  intervals.  These  guys  should  attach  about  one- 
third  of  the  height  from  the  top,  and  are  best  secured  to  a  band 
placed  around  the  ch  mney,  or  to  special  fastenings  so  shaped  and 
riveted  as  to  distribute  the  pull  of  the  guy  over  as  great  an  area 
as  possible.*  When  of  the  self-supporting  class  the  stack  can  be 
held  down  by  anchor-bolts  pass'ng  through  the  base-ring  into  the 

*  Guys  on  stacks  90  feet  high  or  more  should  be  arranged  in  double  sets, 
fastened  at  different  heights. 


CHIMNEY  DESIGN 


333 


foundation,  which  is  generally  about  one-tenth  or  one-eighth  the 
height  of  stack.     Many  designs  are  so  stiff,  however,  as  not  to 


FIG.  150. — Cast-iron  Cap  for  Fig.  148. 

require  support  from  these  anchor-bolts,  although  it  is  always  well 
to  use  them.     The  base  sect:on  is  generally  bell-shaped,  having  a 


334 


STEAM-BOILERS 


bottom  diameter  about  twice 
that  at  top  of  bell  and  a  height 
equal  to  the  bottom  diameter. 

Steel  stacks  should  be  lined 
with  brick,  as  the  lining  pro- 
longs the  life  of  the  metal 
and  materially  adds  to  the 
stability  of  the  structure.  In 
short  or  unimportant  stacks 
the  lining  is  frequently 
omitted. 

In  large  stacks  it  is  ad- 
visable to  build  the  lining  in 
self-supporting  sections  to 
facilitate  renewals,  and  to 
prevent  a  general  failure  due 
to  disintegration.  These  sec- 
tions are  usually  made  from 
12  to  20  feet  in  height. 

The  remarks  on  the 
shape  of  the  top,  the  en- 
trances for  flues  and  clean- 
out,  and  ladder  are  equally 
applicable  to  steel  as  to 
brick  stacks. 

Plates  thinner  than  |  inch 
are  seldom  used,*  on  account 
of  the  weakening  by  corro- 
sion. The  size  of  rivet  for 
varying  thickness  of  plate 
should  be  about  the  same  as 
for  boiler-shells,  but  never  less 
than  J-inch  in  diameter.  The 
pitch  of  rivets  may  be  as  given 
in  Table  XVIII,  although  it 


*  Except  in  stacks  less  than  40 
feet  in  height  and  not  over  20 
inches  hi  diameter. 


SHELF  RING  FOR  HOLDING 
THE  LINING  IN  SECTIONS 


FIG.  151.— Self-supporting  Steel  Stack. 


CHIMNEY  DESIGN  335 

is  usually  somewhat  greater.  For  the  first  50  feet  from  the  top  the 
horizontal  seams  can  be  single-riveted;  for  the  next  150  feet,  double- 
riveted;  and  for  any  additional  length,  treble- riveted.  The  verti- 
cal seams  can  be  single-riveted  for  the  first  100  feet  from  the  top 
and  double-riveted  for  any  additional  length.  The  plating  should 
be  well  lapped  at  the  seams,  and  be  calked  to  prevent  air  leaks. 

In  self-supporting  stacks  the  factor  of  safety  for  the  holding 
down  bolts  should  be  at  least  four,  and  only  half  the  bolts  should 
be  considered  as  in  tension  at  one  time.  These  bolts  should  not 
be  spaced  over  four  feet  apart,  and  there  should  never  be  less  than 
four.  If  additional  bolts  are  used,  the  total  number  is  usually 
a  multiple  of  three  or  four — thus  four,  six,  eight,  nine,  etc. 

The  thickness  of  the  plating  can  be  proportioned  by  the  follow- 
ing formulae,  the  safe  fibre  stress  being  taken  at  10,000  pounds  per 
square  inch : 

Stress  per  lineal  inch  )  _  Moment  for  wind  in  inch-pounds  t 
at  any  section        j  ^rX  (diameter  in  inches)2 

r™  .  ,  .     ,  Stress  per  lineal  inch 

Thickness  in  inches    =  ^r-. j-^- — r—    ,   .  .  .     . 

10,000  X  efficiency  of  horizontal  joint 

The  Riter-Conley  Manufacturing  Co.*  use  a  similar  formula, 

M 

namely,  S=       ,2,  but  neglect  the  efficiency  of  joint  and  adopt  8000 

U.o(Z 

pounds  per  unit  stress  if  the  circumferential  seams  are  single- riveted 
and  10,000  pounds  if  double-riveted.  Steel  stacks  as  manufac- 
tured by  this  company  have  proved  satisfactory,  and  possibly  the 
thickness  as  determined  by  the  above  formulae  may  be  greater  than 
required  except  in  very  exposed  locations. 

A  brick  stack  is  illustrated  in  Fig.  148,  a  ladder  in  Fig.  149, 
and  the  cast-iron  cap  in  Fig.  150. 

A  steel  stack  is  illustrated  in  Fig.  151. 

*  Of  Pittsburg,  Pennsylvania.  Kindness  of  Mr.  Wm.  C.  Coffin,  Vice- 
President,  1903. 


CHAPTER  XV 
SMOKE  PREVENTION 

Losses  Due  to  Smoke.  Public  Nuisance.  Smoke  Ordinances.  Require- 
ments to  Prevent  Smoke.  Prof.  Ringelmann's  Smoke-scales.  Smokeless 
Fuels.  Composition  of  Smoke.  Mixing  Coals.  Air  Admissions.  Hollow 
Bridge.  Extracts  from  Report  by  Prof.  Landreth. 

The  study  of  smoke  prevention  is  intimately  interwoven  with 
that  of  combustion  and  of  boiler  design.  When  combustion  is 
perfect  the  products  of  combustion  are  practically  colorless. 

Smoke  consists  of  soot  or  carbon  in  a  flocculent  state,  mixed 
with  the  products  of  combustion,  namely,  carbon  dioxide,  carbon 
monoxide,  sulphuric  and  sulphurous  acid,  water,  nitrogen,  ammonia, 
carbureted  hydrogen  and  other  vapors  of  lesser  note.  The  losses 
due  to  smoke  generation  are  not  great,  probably  not  exceeding 
in  any  case  more  than  1£  or  2  per  cent  of  the  heat  generated. 
Possibly  the  cost  of  smoke  prevention  with  some  fuels  would 
exceed  the  value  saved  in  heat.  On  the  other  hand,  smoke  can 
be  taken  with  few  exceptions  as  an  evidence  of  uneconomical 
combustion,  whereby  the  real  losses  greatly  exceed  the  above 
figures. 

Smoke  has  become  such  a  public  annoyance  in  closely  peopled 
districts  as  to  warrant  the  officials  of  many  cities  to  pass  prohibi- 
tory ordinances.  Admitting  that  smoke  is  a  public  nuisance,  the 
making  and  enforcing  of  preventive  regulations  appear  to  be  most 
satisfactory  when  they  originate  through  the  local  boards  of  health 
rather  than  by  ordinance,  although  the  smoke  may  not  be  in  suf- 
cient  quantity  as  to  be  injurious  to  health.  The  soot  or  carbon 
is  not  in  itself  injurious,  but  it  is  a  nuisance  when  it  soils  surround- 
ing objects.  The  compounds  of  sulphur  and  ammonia  are  inju- 
rious when  in  quantity,  but  a  smokeless  furnace  may  pass  off  large 
amounts  of  these  products.  Such  regulations  should  be  carefully 
drawn  and  made  to  keep  pace  with  the  advances  being  continually 


SMOKE    PREVENTION  337 

made  in  steam  engineering.  They  should  be  on  some  fair-minded 
penalty  basis,  founded  on  what  can  be  done  commercially  without 
inflicting  too  heavy  a  loss  or  expense,  rather  than  what  could  be 
done  by  compulsion. 

Almost  any  fuel  can  be  consumed  so  as  to  produce  little  or  no 
smoke.  This  is  not  the  case  with  fuels  burned  in  furnaces  designed 
and  set  for  one  grade  and  consuming  another;  nor  in  combustion- 
chambers  so  built  as  to  be  ill  adapted  to  encourage  perfect  com- 
bustion. Due  to  commercial  changes,  some  steam-generating 
localities  are  using  soft  coals,  in  which  hard  coals  were  used  almost 
exclusively  some  few  years  ago.  The  same  boilers,  same  settings 
and  same  methods  of  firing  no  doubt  are  still  largely  employed, 
irrespectively  of  the  changed  conditions.  It  is  not  the  fault  of  the 
fuel  that  smoke  under  such  circumstances  is  produced. 

The  heating  surfaces  of  the  boiler  rob  the  products  of  combus- 
tion of  their  heat,  and  thus  reduce  their  temperature  below  that 
necessary  for  chemical  union  with  the  oxygen.  If  the  constituent 
particles  of  the  fuel  have  not  been  mixed  with  the  incoming  oxygen 
before  this  reduction  of  temperature,  the  carbon,  in  a  finely  divided 
state,  will  pass  off  with  the  draft  and  create  smoke.  To  prevent 
smoke,  therefore,  the  requirements  are  those  conditions  which  will 
furnish  perfect  combustion,  namely,  a  good  draft,  a  proper  mixing 
of  the  air  and  fuel,  and  a  maintenance  of  the  high  temperatures 
until  the  chemical  unions  are  completed.  These  conditions  would 
be  easy  to  obtain  in  a  suitable  furnace  if  it  were  not  for  the  short- 
ness of  time  available. 

Smokeless  fuels,  such  as  oil,  cannot  be  considered  at  this  time 
as  a  substitute  for  the  smoke- producing  fuels,  since  they  are  not 
found  in  sufficient  quantity  to  supply  the  demand  and  the  artificial 
fuels  are  still  too  costly.  Anthracite,  unfortunately,  is  too  expen- 
sive to  compete  with  the  soft  or  smoking  coals.  It  has  been 
shown  on  trial  that  a  combination  of  oil  and  bituminous  coal  can 
be  used  so  as  to  produce  a  practically  smokeless  fire,  but  this  com- 
bination, however,  has  not  proved  very  successful  commercially. 

Bituminous  coal  in  selected  sizes — about  3-inch  cubes — can  be 
burned  practically  smokeless.  Smoke  from  bituminous  coal  can 
be  reduced  by  mixing  50  per  cent  of  anthracite  pea  or  coke  with 
the  bituminous  coal.  The  object  of  the  mixing  is  to  separate  the 
bituminous  coal,  so  that  air  can  reach  every  particle. 


338  STEAM-BOILERS 

Mechanical  stokers  and  down-draft  furnaces  under  suitable 
conditions  reduce  the  amount  of  smoke  visible  to  the  eye,  but  do 
not  lessen  the  other  ingredients  beyond  their  tendency  to  assist 
combustion.  As  the  best-known  mechanical  means  of  firing  are 
incapable  of  lessening  the  compounds  of  sulphur  and  ammonia,  it 
has  been  suggested  that  the  true  solution  of  smoke  prevention 
would  be  to  reduce  the  coal  to  gas  and  then  purify  it  before  use. 
This  solution  may  come  in  time,  especially  for  thickly  settled  manu- 
facturing districts,  but  cannot  be  forced. 

If  an  ordinary  grate  is  used  with  bituminous  coal,  there  should 
be  not  less  than  36  inches  between  grate  and  boiler  surface.  A 
greater  distance  would  be  still  better,  especially  when  very  smoky 
coals  are  used.  Some  grates  produce  smoke  from  a  lack  of  air  open- 
ings. These  openings  for  smoky  coals  should  aggregate  between 
50  and  70  per  cent  of  the  grate  surface.  Air  should  also  be  admit- 
ted above  the  fire,  especially  when  each  charge  of  fresh  coal  is 
fired.  The  air  is  usually  admitted  through  holes  in  the  door  or  in 
the  furnace  front.  As  the  air  is  more  efficient  when  heated,  it  can 
be  made  to  circulate  through  a  space  left  in  the  brick  setting  or  be 
drawn  from  the  ash-pit.  In  such  cases  it  can  be  admitted  through 
holes  in  the  furnace  sides  or  through  a  hollow  bridge  wall.  The 
bridge  of  brick  can  be  made  hollow  and  draw  its  supply  of  air  from 
the  ash-pit,  always  under  control  by  a  damper,  whose  handle 
reaches  back  to  the  fire-room  front.  Some  of  the  brick  courses 
on  the  combustion-chamber  side  and  near  the  top  can  be  set  about 
^-inch  apart  without  cement  between  them.  The  heated  air  can 
thus  pass  out  of  these  openings  in  fine  streams  and  mix  with  the 
products  as  they  pass  over  the  wall. 

Probably  the  best  arrangement  is  to  admit  the  air  both  through 
the  door  openings  and  at  the  bridge  wall,  thus  facilitating  the  mix- 
ing by  adopting  a  number  of  openings.  A  steam  jet  may  be  util- 
ized to  insure  a  thorough  mixing,  but  such  an  arrangement  is  not 
economical. 

When  coals  are  very  smoky  they  should  be  fired  in  small  quan- 
tities at  frequent  intervals  on  the  "alternate"  firing  plan.  In 
cases  of  lack  of  grate  area,  necessitating  high  rates  of  combustion, 
little  can  be  done  when  the  design  is  defective,  except  a  general 
remodelling  of  the  furnace. 

The  degree  of  smoke  produced  at  any  instant  can  be  easily 


SMOKE  PREVENTION 


339 


and  well  recorded  by  using  Prof.  Ringelmann's  smoke-scales, 
described  in  Engineering  News,  11  November,  1897.  The  cards 
should  be  about  8  inches  square,  and  can  be  reproduced  by  a 
draftsman  according  to  the  following  scheme,  Fig.  152 :  * 


No.  1. 


No.  2. 


No.  3.  No.  4. 

FIG.  152. — Prof.  Ringelmann's  Smoke-scales. 
Card  No.  0.     All  white. 

Card  No.  1.  Black  lines,  1  mm.  thick,  10  mm.  apart,  leaving 
spaces  9  mm.  square. 

Card  No.  2.  Black  lines,  2.3  mm.  thick,  leaving  spaces  7.7  mm. 
square. 

Card  No.  3.  Black  lines,  3.7  mm.  thick,  leaving  spaces  6.3  mm. 
square. 

*  Bryan  Donkin  advocated  the  use  of  tinted  cards,  each  having  a  flat 
wash  of  gray  corresponding  to  the  effect  of  the  lines  on  the  Ringelmann 
cards. 


340  STEAM-BOILERS 

Card  No.  4.  Black  lines,  5.5  mm.  thick,  leaving  spaces  4.5  mm. 
square. 

Card  No.  5.     All  black. 

The  observer  glances  from  the  smoke  issuing  from  the  stack 
to  the  cards,  and  determines  which  card  most  nearly  corresponds 
with  the  color  of  the  smoke,  and  makes  a  record  accordingly,  noting 
the  time  when  the  observation  was  made.  Observations  should 
be  made  continuously  during,  say,  one  minute  and  the  estimated 
average  density  during  that  minute  recorded,  and  so  on,  records 
being  made  once  every  minute.  The  average  of  all  the  records 
taken  is  the  average  for  the  smoke  density.  When  these  minute 
records  are  taken  over  a  sufficiently  long  period,  the  whole  can  be 
plotted  on  section  paper  to  show  by  a  curve  or  broken  line  how  the 
smoke  density  varied  during  that  period. 

The  following  is  an  extract  from  a  report  *  to  the  State  Board 
of  Health  of  Tennessee  on  "  Smoke  Prevention,"  by  Prof.  Olin  A. 
Landreth,  of  Vanderbilt  University,  1893: 

"  When  fresh  coal  is  thrown  on  a  bed  of  incandescent  coal,  or  is 
otherwise  highly  heated,  there  immediately  begins  the  distillation 
of  the  more  volatile  portions  of  the  hydrocarbons  in  the  coal, 
which  distilled  matter  is  burned  if  the  temperature  is  high  enough 
and  a  sufficient  supply  of  oxygen  is  present,  but  which  passes  up 
the  chimney  as  yellowish  fumes  if  either  of  these  two  essential 
conditions  of  combustion  is  wanting.  As  the  fresh  coal  becomes 
more  highly  heated  the  less  volatile  hydrocarbons  are  distilled,  and 
these  being,  chemically  speaking,  unstable  compounds,  are  de- 
composed or  disassociated  by  the  heat  at  a  temperature  much 
below  that  at  which  the  carbon  thus  liberated  combines  with 
oxygen  in  combustion.  The  temperature  necessary  for  combustion 
of  this  free  carbon  is  very  high,  approximately  2000  degrees  Fahr., 
and  hence  there  is  a  wide  margin  of  opportunity  for  this  portion 
of  the  carbon  to  escape  unburned,  as  this  temperature  is  somewhat 
difficult  to  maintain  in  the  mass  of  gaseous  matter  above  the  coal. 

"  It  is  this  free,  unburned  carbon  in  a  finely  divided  state  which 
produces  the  bright,  luminous  flame,  and  which,  when  cooled, 
produces  the  black  clouds  of  smoke  that  issue  from  the  chimney 
and  which  afterward  settle  as  soot.  After  the  volatile  matter  is 
all  driven  off,  there  still  remains  the  fixed  carbon,  which  now  is  in 

*  Engineering  News,  8  June,  1893. 


SMOKE  PREVENTION  341 

the  form  of  coke.  This  gives  but  little  flame,  and  no  smoke  in 
burning,  as  the  particles  are  not  detached  from  the  solid  mass 
till  combustion  takes  place. 

"The  causes  of  smoke  may,  from  the  foregoing  description,  be 
stated  to  be  either 

"(1)  An  insufficient  amount  of  oxygen  for  the  perfect  combus- 
tion of  these  combustibles;  or 

"(2)  An  imperfect  mixture  or  distribution  of  the  oxygen  with 
the  combustibles,  even  though  present  in  sufficient  quantity;  or 

"(3)  A  temperature  too  low  to  ignite  the  distilled  volatile 
matter  and  the  separated  free  carbon  when  properly  mixed  with 
the  air. 

"  In  the  ordinary  boiler  furnace,  as  generally  constructed  and 
fired,  the  conditions  are  very  unfavorable  for  perfect  combustion 
during  the  period  in  which  the  volatile  matter  is  driven  off  from 
each  charge  of  coal.  When  the  fixed  carbon  stage  is  reached  there 
is  but  little  difficulty  in  maintaining  perfect  combustion,  but  when 
a  fresh  charge  of  coal  is  added  the  difficulties  reappear;  the  air- 
supply,  if  not  in  excess  during  the  burning  of  the  previous  incan- 
descent coal,  will  now  be  in  deficit,  since  the  distillation  of  the 
volatile  matter  calls  for  an  increased  amount  of  air,  while,  in  fact, 
the  greater  depth  of  coal  now  on  the  grate  actually  reduces  the 
supply. 

"  If  an  additional  supply  is  admitted  through  the  furnace  doors, 
it  will  be  cold,  and  cannot  be  thoroughly  mixed  with  the  com- 
bustible gases.  So  with  the  temperature;  if  high  enough  before 
charging,  it  is  now  much  lower  owing  to  the  cooling  effects  of  the 
cold  air  rushing  in  when  the  doors  are  opened,  of  the  mass  of  cold 
coal,  of  the  evaporation  of  the  moisture  in  the  coal  and  to  the  dis- 
tillation of  the  volatile  matter,  so  that  by  the  time  a  high  tempera- 
ture is  needed  to  burn  the  free  carbon  the  furnace  is  at  its  coldest, 

"  In  fulfilling  the  requirements  of  sufficiency  of  supply,  and 
thoroughness  of  mixing  the  air  with  the  combustible  gases,  it  must 
be  noted  that  the  conditions  should  not  be  secured  by  a  reckless 
surplus  of  air,  as  this  carries  away  useful  heat  which  is  not  only 
a  loss  in  itself,  but  may,  and  often  does,  result  in  lowering  the 
temperature  of  the  combustible  gases  below  their  temperature  of 
ignition,  thus  causing  the  escape  of  unburned  fuel.  Owing  to  the 
difficulty  of  effecting  such  a  thorough  mixture,  so  as  to  bring  to 


342  STEAM-BOILERS 

each  combustible  particle  just  its  proper  amount  of  air,  it  is  neces- 
sary to  provide  a  surplus  of  air,  but  this  should  be  considered 
as  an  evil  to  be  kept  at  a  minimum  by  the  most  thorough  mixing 
possible. 

"  Passing  to  the  means  of  accomplishing  combustion  without 
smoke  production,  it  is  safe  to  say  that,  so  far  as'  it  pertains  to 
steam-boilers,  the  object  must  be  attained  by  one  or  more  of  the 
following  agencies : 

"  1.  By  the  proper  design  and  setting  of  the  boiler  plant.  This 
implies  proper  grate  area,  sufficient  draft,  the  necessary  air  admis- 
sion space  between  grate-bars  and  through  furnace,  and  ample 
combustion  room  under  boilers. 

"2.  By  that  system  of  firing  that  is  best  adapted  to  each  par- 
ticular furnace  to  secure  the  perfect  combust  on  of  bituminous 
coal.  This  may  be  either  (a)  '  Coke  firing/  or  charging  all  coal 
into  the  front  of  the  furnace  until  partially  coked,  and  then  push- 
ing back  or  spreading;  or  (6)  'Alternate  side-firing';  or  (c) 
'  Spreading/  by  which  the  coal  is  spread  over  the  whole  grate 
area  in  thin,  uniform  layers  at  each  charging. 

"  3.  The  admission  of  air  through  the  furnace  door,  bridge  wall 
or  side  walls. 

"  4.  Steam  jets  and  other  artificial  means  of  thoroughly  mix- 
ing the  air  and  combustible  gases. 

"  5.  Prevention  of  the  cooling  of  the  furnace  and  boilers  by  the 
inrush  of  cold  air  when  the  furnace  doors  are  opened  for  charging 
coal  and  handling  the  fire. 

"  6.  Establishing  a  gradation  of  the  several  steps  of  combus- 
tion, so  that  the  coal  may  be  charged,  dried  and  warmed  at  the 
coolest  part  of  the  furnace,  and  then  moved  by  successive  steps 
to  the  hottest  place,  where  the  final  combustion  of  the  coked  coal 
is  completed,  and  compelling  the  distilled  combustible  gases  to 
pass  through  the  hottest  part  of  the  fire. 

"  7.  Preventing  the  cooling  by  radiation  of  the  unburned  com- 
bustible gases  until  perfect  mixing  and  combustion  have  been 
accomplished. 

"  8.  Varying  the  supply  of  air  to  suit  the  periodic  variation  in 
demand. 

"9.  The  substitution  of  a  continuous  uniform  feeding  of  coal 
instead  of  intermittent  charges. 


SMOKE   PREVENTION  343 

"  10.  Down-draft  burning,  or  causing  the  air  to  enter  above 
the  grates  and  pass  down  through  the  coal,  carrying  the  distilled 
products  down  to  the  high-temperature  plane  at  the  bottom  of  the 
fire. 

11  The  number  of  smoke-prevention  devices  are  legion.  The  scope 
of  the  present  paper  renders  anything  more  than  a  brief  classifi- 
cation of  their  principles  of  working  impossible.  These  are : 

"(a)  Mechanical  stokers,  which  automatically  deliver  the  fuel 
in  a  crushed  or  finely  divided  state  into  the  furnace  at  a  uniform 
rate,  and  also  keep  the  fire  clean  by  a  slow  but  constant  motion  of 
the  individual  sections  of  the  grate.  They  accomplish  their  object 
by  means  of  agencies  5,  6  and  9  of  the  foregoing  list.  They  affect 
a  very  material  saving  in  the  labor  of  firing,  and  are  efficient  smoke 
preventers  when  not  pushed  above  their  capacity,  and  when  the 
coal  does  not  cake  badly.  They  are  rarely  susceptible  to  the 
sudden  changes  in  the  rate  of  firing  frequently  demanded  in 
service. 

"(b)  Air-flues  in  side  walls,  bridge  wall  and  grate-bars,  through 
which  air,  when  passing,  is  heated  (agency  3).  The  results  are 
always  beneficial,  but  the  flues  are  difficult  to  keep  clean  and  in 
order. 

"(c)  Coking  arches,  or  spaces  in  front  of  the  furnace  arched  over, 
in  which  the  fresh  coal  is  coked,  both  to  prevent  cooling  of  the  dis- 
tilled gases  and  to  force  them  to  pass  through  the  hottest  part  of 
the  furnace,  just  beyond  the  arch  (agencies  6  and  7).  The  results 
.are  good  for  normal  conditions,  but  ineffective  when  the  fires  are 
forced.  The  arches  also  are  easily  burned  out  and  injured  by 
working  the  fire. 

"(d)  Dead-plates,  or  a  portion  of  the  grate  next  to  the  furnace 
doors  reserved  for  warming  and  coking  the  coal  before  it  is  spread 
over  the  grate  (agency  6).  These  give  good  results  when  the  fur- 
nace is  not  forced  above  its  normal  capacity.  This  embodies  the 
method  of  '  coke-firing'  mentioned  above. 

"(e)  Down-draft  furnaces,  or  furnaces  in  which  the  air  is  supplied 
to  the  coal  above  the  grate,  and  the  products  of  combustion  are  car- 
ried away  beneath  the  grate,  thus  causing  a  downward  draft  through 
the  coal,  carrying  the  distilled  gases  down  the  highly  heated  incan- 
descent coal  at  the  bottom  of  the  layer  of  coal  on  the  grate  (agency 
10).  In  this  furnace  the  grate-bars  must  be  kept  cool  by  the  cir- 


344  STEAM-BOILERS 

dilation  of  water  through  them,  as  they  have  to  bear  the  hottest 
portion  of  the  flame. 

"(/)  Steam  jets  to  draw  air  in,  or  inject  air  into  the  furnace 
above  the  grate,  and  also  to  mix  the  air  and  combustible  gases 
together  (agency  4).  A  very  efficient  smoke  preventer,  but  one 
liable  to  be  wasteful  of  fuel  by  inducing  too  rapid  a  draft. 

"(g)  Baffle  plates  placed  in  the  furnace  above  the  fire,  to  aid  in 
mixing  the  combustible  gases  with  the  air  (agency  4) . 

"(h)  Double  furnaces,  of  which  there  are  two  entirely  different 
styles,  the  first  of  which  places  the  second  grate  below  the  first 
grate;  the  coal  is  coked  on  the  first  grate;  during  the  process  the 
distilled  gases  are  made  to  pass  over  the  second  grate,  where  they 
are  ignited  and  burned;  the  coke  from  the  first  grate  is  dropped 
on  to  the  second  grate  (agencies  6  and  7).  A  very  efficient  and 
economical  smoke  preventer,  but  rather  complicated  to  construct 
and  maintain.  In  the  second  form,  the  products  of  combustion 
from  the  first  furnace  pass  through  the  grate  and  fire  of  the 
second,  each  furnace  being  charged  with  fresh  fuel  when  needed, 
the  latter  generally  with  a  smokeless  coal  or  coke.  An  irrational 
and  unpromising  method. 

"  It  is  no  longer  a  problem  whether  smoke  can  be  prevented  or 
not.  This  has  been  settled  conclusively  in  the  affirmative  in  a 
number  of  localities  where  proper  laws  for  the  abatement  of  smoke 
have  been  passed  and  enforced.'! 


CHAPTER  XVI 
TESTING.     BOILER  COVERINGS.     CARE  OF  BOILERS 

Object  of  Testing  New  Boilers.  Hydraulic  Pressure.  Methods  Adopted. 
Measuring  for  Changes  of  Form.  Limit  of  Test  Pressure.  Testing  for  Steam 
Leaks.  Boiler  Trials.  Directions  for  Calculating  Some  Results.  Boiler 
and  Pipe  Coverings.  Heat  Losses.  Savings.  Care  of  Boilers. 

Testing.  Boilers  should  always  be  tested  before  being  accepted 
from  the  maker,  but  it  should  be  remembered  that  the  test  is  for 
the  purpose  of  exposing  faults,  defects  or  leaks  rather  than  of 
proving  the  strength  of  the  structure.  Many  a  good  boiler  has 
been  ruined  by  being  overstrained  during  its  initial  test. 

Testing  is  always  done  by  the  application  of  pressure.  As 
testing  by  steam  is  dangerous  and  not  to  be  tolerated,  hydraulic 
pressure  has  been  almost  universally  adopted.  The  boiler  can  be 
filled  with  water,  the  valve  closed,  and  a  light  fire  built  so  as  to 
warm  the  water,  the  pressure  due  to  the  expansion  being  noted  on 
the  gauge.  When  the  required  pressure  has  been  reached,  the 
valve  should  be  slightly  opened  so  as  to  maintain  it  or  relieve  it. 
As  by  this  method  it  is  difficult  to  control  the  pressure  and  make 
furnace  measurements,  a  simpler  plan  is  to  fill  the  boiler  with  hot 
water  and  maintain  the  pressure  for  a  few  minutes  by  means  of  a 
pump.  If  the  pressure  falls  rapidly  there  is  indication  of  a  leak, 
for  which  search  should  be  made. 

While  under  pressure,  the  boiler  should  be  very  closely  examined 
for  change  of  form.  Careful  measurements  should  be  made  before, 
during  and  after  the  test,  and  any  change  of  form  noted.  If  any 
permanent  set  is  detected,  care  must  be  used  to  determine  if  it  is 
due  to  an  excess  of  the  elastic  limit  of  the  material  or  to  a  tighten- 
ing of  the  joints  of  stays  and  braces.  If  the  flues  show  any  ten- 
dency to  flatten,  such  results  must  always  be  treated  with  great 
caution,  since  the  defect  is  liable  to  become  aggravated.  Too 

345 


346  STEAM-BOILERS 

hot  water  cannot  be  used  if  accurate  measurements  are  to  be  made, 
unless  the  boiler  be  heated  before  the  first  measurements  are  taken. 

The  limiting  pressure  for  tests  is  usually  placed  at  one  and 
one-half  the  highest  steam  pressure  to  be  carried.  Many  con- 
demn this  measure  of  test  pressure  and  advocate  some  fixed  increase 
above  the  highest  working  pressure  as  being  more  equitable;  as 
for  instance  a  test  pressure  to  be  the  highest  working  pressure 
plus  90  pounds  on  the  square  inch.  However,  it  is  best  not  to 
allow,  even  in  the  best  made  boilers,  a  test  pressure  to  exceed 
40  per  cent  of  the  calculated  strength  of  the  weakest  riveted  joint. 

Before  a  boiler  is  finally  covered  with  lagging,  but  after  it  has 
been  set  and  all  connected,  steam  should  be  raised  and  leaks  searched 
for.  Most  new  boilers  leak  under  steam,  even  after  having  proved 
tight  under  an  hydrostatic  test.  Generally  small  leaks  will  close 
of  their  own  accord,  although  ordinary  leaks  require  calking  after 
the  steam  pressure  has  been  relieved.  If  the  leaks  are  due  to  a 
defect  in  design,  their  closure  is  frequently  a  difficult  matter.  Care 
in  working  out  details  and  in  construction  will  be  repaid  many 
times  over  in  preventing  such  annoyances. 

Boiler  Trials.  Boilers  are  frequently  tested  when  completed 
for  obtaining  data  as  to  their  actual  performance.  Such  tests 
are  termed  "  trials."  The  data  should  be  collected  by  trained 
assistants  and  only  calibrated  instruments  used.  The  object  for 
which  the  trial  is  being  made  should  always  be  clearly  defined  in 
advance,  and  all  data  bearing  on  the  desired  result  be  recorded 
by  the  assistants,  who  should  work  according  to  some  prearranged 
plan. 

For  full  information  of  how  to  carry  out  a  boiler  trial,  reference 
is  made  to  the  "  Report  of  the  Committee  on  the  Revision  of  the 
Society  Code  of  1885,  relative  to  a  Standard  Method  of  Conducting 
Steam-boiler  Trials/'  being  the  code  of  the  American  Society  of 
Mechanical  Engineers  and  published  in  the  Society's  Transactions, 
Vol.  XXI,  1900.  As  this  report  is  too  voluminous  to  reprint  in  full, 
and  as  copies  are  obtainable  from  the  Secretary  of  the  Society, 
the  following  may  prove  useful,  being  an  extract  from  "  Experimen- 
tal Mechanics,"  by  D.  S.  Jacobus,  Stevens  Institute  Indicator,  and 
from  the  Am.  Soc.  M.  E.  Code. 

Directions  for  Calculating  Some  Results  Derived  from  Trial. 
Total  combustible  =  total  dry  coal  consumed  minus  weight  of  refuse. 


TESTING  347 

(Ordinarily  the  refuse  is  the  ash  and  unburned  coal  raked  out  from 
the  ash-pit.) 

Per  cent  of  ash  =  weight  of  ash  X 100-?-  total  coal  consumed. 

Rate  of  combustion  in  pounds  per  sq.  ft.  of  grate  per  hour  =  total 
€oal  consumed  in  Ibs.  divided  by  the  length  of  test  in  hours  and 
the  grate  area  in  square  feet. 

The  weight  of  water  evaporated  at  actual  boiler  pressure  is  the 
total  amount  of  water  fed  to  the  boilers  less  the  entrained  water. 
The  total  weight  of  entrained  water  cannot  be  determined  with  a 
calorimeter  having  the  usual  form  of  collecting  nipple  arranged 
so  as  to  draw  out  a  small  amount  of  steam  from  the  steam-main, 
because  the  sample  of  steam  collected  and  passed  into  the  calori- 
meter may  not  be  an  average  of  the  total  amount  flowing  through 
the  steam-main.  Small  throttling  calorimeters  are  reliable,  how- 
ever, in  showing  whether  the  steam  contains  a  considerable  amount 
of  moisture  or  is  practically  dry,  and  this  is  especially  so  if  they 
are  used  in  combination  with  an  adjustable  nozzle,  which  can  be 
made  to  draw  out  a  sample  from  any  desired  point  in  the  cross- 
section  of  the  pipe.  To  allow  properly  for  the  entrained  water, 
the  entire  amount  should  be  separated  from  the  steam  and  weighed, 
or  the  entire  mass  of  steam  may,  in  special  cases,  be  passed  through 
a  throttle-valve  and  exhausted  at  atmospheric  pressure,  and  from 
the  temperature  of  steam  after  throttling,  the  percentage  of  moisture 
can  be  calculated  in  the  same  way  as  for  a  throttling  calorimeter. 
It  must  not  be  inferred  from  this  that  small  throttling  calorimeters 
are  not  useful  in  boiler  tests.  They  should  always  be  applied,  if 
the  steam  is  not  found  to  be  superheated;  and  if  they  indicate 
dry  steam  for  samples  taken  from  all  sections  of  the  pipe,  or  when 
a  fixed  nozzle  is  placed  in  such  a  position  that  any  moisture  in  the 
steam  would  be  thoroughly  ming'ed  and  would  be  drawn  into  the 
nozzle,  they  prove  definitely  that  the  steam  is  dry. 
Let  t  =  temperature  of  feed-water, 

H  =  the  total  heat  of  steam  at  the  boiler  pressure  above  32°  F.; 
and     W  =  weight  of  water  actually  evaporated ; 
then 

Equivalent  evaporation  from  and  at  212°  F.  =  W    ~  1~       , 

9oo .  7 

where  965.7  is  the  latent  heat  of  steam  at  atmospheric  pressure. 
This  equation  is  for  dry  saturated  steam.     If  the  steam  is  super- 


348  STEAM-BOILERS 

heated  the  actual  evaporation  must  be  multiplied  by  the  factor 

tf  . 
—  ,  in  which  F  is  the  superheating  in  degrees  .banr. 


.  7 

The  horse-power  of  the  boiler,  according  to  the  standard  of  the 
American  Society  of  Mechanical  Engineers,  is  found  by  dividing 
the  equivalent  evaporation  from  and  at  212°  F.  by  34.5. 

The  following  is  the  formula  for  calculating  the  percentage  of 
moisture  in  the  steam  when  a  throttling  calorimeter  is  used  : 


in  which  w  =  percentage  of  moisture  in  the  steam,  H  =  total  heat, 
L  =  latent  heat  per  pound  of  steam  at  the  pressure  in  the  steam- 
pipe,  h  =  total  heat  per  pound  of  steam  at  the  pressure  in  the  dis- 
charge side  of  the  calorimeter,  k  =  specific  heat  of  superheated 
steam,  T  =  temperature  of  the  throttled  and  superheated  steam 
in  the  calorimeter,  and  £  =  temperature  due  to  the  pressure  in  the 
discharge  side  of  the  calorimeter,  =  212°  F.  at  atmospheric  pressure. 
Taking  A;  =  0.48  and  £  =  212,  the  formula  reduces  to 


A  correction  should  be  made  for  radiation  from  the  surface  of 
the  instrument.  This  loss,  according  to  George  H.  Barrus,  amounts 
to  about  three-tenths  of  one  per  cent  of  moisture. 

The  following  is  the  formula  for  calculating  the  moisture  in 
the  steam  when  a  barrel  calorimeter  is  used : 

Let  W  =  the  original  weight  of  the  water  in  calorimeter, 

w  =  the  weight  of  water  added  to  the  calorimeter  by  blow- 
ing steam  into  the  water, 

t  =  total   heat   of   water   corresponding   to   initial   tem- 
perature of  water  in  calorimeter, 
tv  =  total  heat  of  water  corresponding  to  final  temperature 

in  calorimeter, 
T1  =  total  heat  in  the  water  at  the  temperature  due  to  the 

steam  pressure, 

(This  is  nearly  equal  to  the  temperature  of  the  steam 
less  32  degrees.) 


TESTING  349 

H= total  heat  of  steam  due  to  the  steam  pressure, 
x  =  pounds  of  steam  blown  into  calorimeter, 
y  =  percentage  of  priming, 
k  =  degrees  of  superheating; 
then 


w 


An  approximate  "  heat  balance,"  that  is,  a  statement  of  the 
distribution  of  the  heating  value  of  the  coal,  may  be  reported  in 
the  form  given  on  page  350. 

The  weight  of  air  per  pound  of  carbon  burned  is  given  by  the 
formula 

7N 


3(CO,+  CO) 


-^0.77; 


where  N,  C02  and  CO  represent  the  average  per  cents  by 
volume  of  the  several  gases  given  by  the  analysis.  This  formula 
is  approximate  on  account  of  the  fact  that  the  percentage  of  nitro- 
gen in  the  coal  is  neglected.  The  error  due  to  this  cause  is,  how- 
ever, a  very  small  one,  and  the  formula  is  much  more  accurate 
than  a  similar  formula  based  on  the  ratio  of  the  oxygen  in  the 
flue  gas  to  the  total  carbon. 

To  find  the  amount  of  carbon  burned  per  pound  of  coal,  deduct 
from  the  total  per  cent  of  carbon  determined  by  the  analysis  the 
percentage  of  unconsumed  carbon  contained  in  the  ash.  This 
percentage  of  unconsumed  carbon  in  the  ash  is  equal  to  the  per- 
centage of  the  ash  as  determined  in  the  boiler  test  less  the  per- 
centage of  ash  determined  by  analysis.  For  example,  if  the  ash 
in  the  boiler  test  were  16  per  cent  and  by  analysis  12  per  cent, 
the  percentage  of  carbon  unconsumed  would  be  4  per  cent  of  the 
coal  burned.  If  there  were  80  per  cent  of  carbon  in  the  coal  the 


350 


STEAM-BOILERS 


HEAT  BALANCE,  OR  DISTRIBUTION  OF  THE  HEATING  VALUE  OF  THE 

COMBUSTIBLE. 
Total  Heat  Value  of  1  Ib.  of  Combustible . .  .  .  B.  T.  U. 


1.     Heat  absorbed  by  the  boiler  =  evaporation  from  and  at 

212  degrees  per  pound  of  combustible  X  965. 7. 
Loss  due  to  moisture  in  coal  =  per  cent  of  moisture  re- 
ferred    to     combustible  -f- 100  X  [(212-  0  +  966+  0.48 
(T  —  212)]  (1=  temperature  of  air  in  the  boiler-room, 
T=that  of  the  flue  gases). 

Loss  due  to  moisture  formed  by  the  burning  of  hydro- 
gen =per  cent  of  hydrogen  to  combustible  ^100~X  9  X 
[(212-0+ 966+0. 48(7'- 212)]. 

4.*  Loss  due  to  heat  carried  away  in  the  dry  chimney  gases 
= weight  of  gas  per  pound  of  combustible  XO.  24  X 
(T-t). 

5.f  Loss    due    to    incomplete    combustion    of    carbon  = 
CO  per  cent  C  in  combustible 

ovFcox  100 

Loss  due  to  unconsumed  hydrogen  and  hydrocarbons, 
to  heating  the  moisture  in  the  air,  to  radiation,  and 
unaccounted  for.  (Some  of  these  losses  may  be  sepa- 
rately itemized  if  data  are  obtained  from  which  they 
may  be  calculated.) 


2. 


3. 


6. 


Totals. . 


B.  T.  U. 

Per  Cent. 

100.00 

*  The  weight  of  gas  per  pound  of  carbon  burned  may  be  calculated  from  the  gas  analyses 
as    follows: 

11C02  +  8O+7(CO  +  N) 
Dry  gas  per  pound  carbon  =  -       — 3(^0  +CO) 


-,  in  which  CO2,  CO,  O  and  N  are 


the  percentages  by  volume  of  the  several  gases.  As  the  sampling  and  analyses  of  the 
gases  in  the  present  state  of  the  art  are  liable  to  considerable  errors,  the  result  of  this 
calculation  is  usually  only  an  approximate  one.  The  heat  balance  itself  is  also  only  approxi- 
mate for  this  reason,  as  well  as  for  the  fact  that  it  is  not  possible  to  determine  accurately 
the  percentage  of  unburned  hydrogen  or  hydrocarbons  in  the  flue  gases. 

The  weight  of  dry  gas  per  pound  of  combustible  is  found  by  multiplying  the  dry  gas 
per  pound  of  carbon  by  the  percentage  of  carbon  in  the  combustible,  and  dividing  by  100. 

t  CO2  and  CO  are  respectively  the  percentage  by  volume  of  carbonic  acid  and  carbonic 
oxide  in  the  flue  gases.  The  quantity  10, 150  =  Number  heat-units  generated  by  burn- 
ing to  carbonic  acid  one  pound  of  carbon  contained  in  carbonic  oxide. 


per  cent  of  carbon  burned  per  pound  of  coal  and  made  to  pass  up 
the  chimney  would  be  80—4  =  76  per  cent.  To  determine  the 
pounds  of  air  per  pound  of  coal,  multiply  the  pounds  of  air  per 
pound  of  carbon  by  the  amount  of  carbon  burned  per  pound  of 
coal,  which,  in  the  case  just  cited,  would  be  0.76. 

Boiler  and  Pipe  Coverings.  All  external  surfaces  of  boilers, 
pipes,  fittings,  etc.,  from  which  loss  of  heat  may  occur  should 
be  well  covered  or  insulated.  The  saving  of  the  heat  often 
pays  for  the  covering  within  one  year.  Good  coverings  cost,  in 


BOILER  COVERINGS  351 

place,  from  17  cents  to  25  cents  per  square  foot  of  metal  surface 
lagged. 

The  selection  of  a  covering  should  depend  upon  absolute  incom- 
bustibility and  freedom  from  all  substances  which  might  cause 
corrosion.  Coverings  which  carbonize  after  being  in  contact  with 
a  hot  surface  or  which  char  when  held  in  a  flame  are  not  fire-proof 
and,  as  a  class,  cannot  be  recommended.  The  best  of  the  cork 
coverings,  however,  have  proved  satisfactory.  Also,  coverings 
which  lose  their  shape  and  form  after  being  some  time  in  use,  such 
as  hair  felt,  cannot  be  classed  as  satisfactory  or  economical. 

The  conclusions  reached  by  the  Mutual  Boiler  Insurance  Com- 
pany, from  tests  made,  were  that  "  there  were  a  sufficient  number 
of  safe,  suitable  and  incombustible  coverings  for  steam  pipes  and 
boilers  .  .  .  without  giving  regard  to  any  of  the  composite 
coverings  which  contain  combustible  material  in  greater  or  lesser 
quantity,  according  to  the  integrity  of  the  makers,  and  without 
giving  regard  to  coverings  which  contain  substances  like  the 
sulphate  of  lime,  which  may  cause  the  dangerous  corrosion 
of  the  metal  against  which  it  is  placed."  (Circular  No.  6,  Boston, 
1898.) 

The  sectional  coverings  are  the  most  convenient  and  can  be 
removed  with  little  injury.  On  large  surfaces  the  sectional  blocks 
are  held  in  place  by  a  wire  netting,  which  should  be  woven  from 
galvanized  wire,  and  the  blocks  coated  with  a  hard-finish  plaster 
applied  about  one-quarter  inch  in  thickness.  This  plaster  coating 
can  be  painted.  On  pipes  the  sectional  coverings  can  be  wrapped 
with  canvas  having  the  edges  sewed  together,  and  the  whole  banded 
if  so  desired  with  brass  or  iron  bands.  These  bands  should  be 
about  12  inches  to  24  inches  apart,  according  to  size  of  pipe.  Irreg- 
ular pieces,  fittings,  valves,  etc.,  are  best  insulated  by  a  plastic 
coating  applied  thick  enough  to  be  even  with  the  sectional  pieces 
on  the  straight  pipes  adjacent. 

A  good  covering  does  not  need  a  layer  of  asbestos  paper  between 
it  and  the  heated  surface. 

Coverings  on  boilers  are  best  placed  directly  against  the  shell 
without  an  air  space,  so  that  any  leak  in  a  joint  or  rivet  will  reveal 
the  spot  and  not  trickle  down  the  air  space  and  appear  at  some 
distant  point. 

The  following  information  has  been  abstracted  from  Transac- 


352 


STEAM-BOILERS 


tions  American  Society  of  Mechanical  Engineers,  Vol.  XIX,  1898 
("  Protection  of  Steam-heated  Surfaces,"  by  C.  L.  Norton). 

TABLE  XXI 


Specimen. 

Name. 

u 

III 

*•*$ 

rr1  ^ 

6*$ 

°£ 
|ffl 

^a 

o 
O«*3 

o  ffi  v 

fJI 

Thick- 
ness in 
Inches. 

Weight  in  Ounces 
per  Ft.  of  Length 
4  In.  Diam. 

A 

Nonpareil  Cork  Standard    .  . 

2  20 

15  9 

1   00 

27 

B 

"            "     Octagonal  .  . 

2  38 

17  2 

80 

16 

C 

Manville  High  Pressure.  .  .  . 

2  38 

17  2 

1  25 

54 

D. 

Magnesia                    

2  45 

17  7 

1  12 

35 

E 

Imperial  Asbestos  

2  49 

18  0 

1   12 

45 

F. 

W  B                            .... 

2  62 

18  9 

1   12 

59 

G 

Asbestos  Air  Cell  .  .            ... 

2  77 

20  0 

1   12 

35 

H.  .  . 

Manville  Infusorial  Earth    .  . 

2  80 

20  2 

1  50 

I. 

"        Low  Pressure  

2  87 

20  7 

1  25 

J  . 

"        Magnesia  Asbestos 

2  88 

20  8 

1  50 

65 

K.  .  .     . 

Magnabestos  

2  91 

21  0 

1   12 

48 

-[J 

Moulded  Sectional  

3  00 

21  7 

1  12 

41 

O..  . 

Asbestos  Fire  Board  

3  33 

24  1 

1  12 

35 

P  

Calcite  

3  61 

26  1 

1  12 

66 

Bare  Pipe 

13  84 

100  0 

Specimen  A  consists  of  granulated  cork  pressed  in  a  mould  at 
high  temperature  and  then  submitted  to  a  fire-proofing  process. 
Made  by  Nonpareil  Cork  Co. 

-  Specimen  B  is  similar  in  composition,  but  is  made  up  of  several 
strips  of  cork  instead  of  two  semi-cylindrical  sections.  Made  by 
Nonpareil  Cork  Co. 

Specimen  C  is  a  sectional  cover  composed  of  an  inner  jacket  of 
earthy  material  and  an  outer  jacket  of  wool  felt,  the  whole  being 
1}  inches  thick.  Made  by  Manville  Co. 

Specimen  D  is  a  moulded  sectional  cover  composed  of  about  90 
per  cent  carbonate  of  magnesia.  Made  by  Keasbey  &  Mattison  Co. 

Specimen  E  is  essentially  an  air-cell  cover,  being  composed  of 
sheets  of  asbestos  paper  which  has  been  indented  before  being  laid 
up,  the  indentations  serving  to  keep  the  thin  sheets  of  paper  from 
coming  in  close  contact  with  one  another,  thereby  causing  a  con- 
siderable amount  of  air  to  be  held  throughout  the  body  of  the  cover. 
Made  by  H.  F.  Watson  Co. 

Specimen  F  is  composed  of  a  wool  felt  with  a  lining  of  asbestos 
paper.  Made  by  H.  F.  Watson  Co. 


BOILER  COVERINGS  353 

Specimen  G  is  a  cover  made  up  of  thin  sheets  of  asbestos  paper 
fluted  or  corrugated  and  stuck  together  with  silicate  of  soda. 
Asbestos  air-cell  cover  of  the  Asbestos  Paper  Co. 

Specimen  H  is  a  plastic  covering  of  infusorial  earth,  made  by 
the  Manville  Co. 

Specimen  I  is  similar  to  specimen  F,  and  made  by  the  Man- 
ville Co. 

Specimen  J  is  a  plastic  cover  made  by  the  Manville  Co. 

Specimen  K  is  a  moulded  cover  containing  about  45  per  cent 
of  carbonate  of  magnesia  and  a  considerable  percentage  of  car- 
bonate of  calcium,  and  made  by  the  Keasbey  &  Mattison  Co. 

Specimen  L  is  a  moulded,  sectional  cover  composed  mainly  of 
sulphate  of  calcium  and  some  25  per  cent  of  carbonate  of  mag- 
nesia and  has  upon  its  outer  surface  a  thick  sheet  of  felt  board. 

Specimen  0  is  similar  to  specimen  G,  except  that  it  has  larger 
cells  and  contains  much  more  silicate  of  soda.  It  is  very  hard  and 
strong.  Made  by  Asbestos  Paper  Co. 

Specimen  P  is  a  sectional  moulded  cover  composed  mainly  of 
sulphate  of  calcium.  It  has  an  outer  layer  of  felt  board.  Made  by 
Philip  Gary  Co. 

Purchasers  should  satisfy  themselves  that  they  are  not  buying 
under  the  name  of  " magnesia"  a  covering  containing  large  quan- 
tities of  sulphate  of  lime,  which  is  liable  to  cause  corrosion.  Mag- 
nesia is  a  most  effective  non-conductor.  Asbestos  is  merely  an 
incombustible  material  in  which  air  may  be  entrapped,  but  when 
not  porous  is  a  good  conductor. 

Table  XXII  gives  the  saving,  in  dollars,  due  to  the  use  of  the 
various  covers. 

Table  XXIII  shows  that  at  the  end  of  ten  years  the  best  of  the 
covers  tested  will  have  saved  $46  more  than  the  poorest.  The 
difference  between  the  several  covers  of  the  better  grade  is  exceed- 
ingly small. 

The  following  assumptions  have  been  made  in  computing  the 
tables : 

That  all  the  covers  cost  $25  per  hundred  square  feet  applied. 
In  case  the  saving  due  to  a  cover  which  costs  $20  instead  of  $25  is 
desired,  the  simple  addition  to  the  final  saving  of  the  $5  difference 
makes  the  necessary  correction. 

The  money  saving  is  computed  on  the  following  assumptions: 


354 


STEAM-BOILERS 


Coal  at  $4  a  ton  evaporates  10  pounds  of  water  per  pound  of  coal. 
The  pipes  are  kept  hot  ten  hours  a  day  three  hundred  and  ten  days 
a  year.  If  computations  are  made,  as  is  sometimes  done,  on  an 
assumption  that  the  pipes  are  hot  twenty-four  hours  a  day  three 
hundred  and  sixty-five  days  a  year,  the  saving  is  nearly  three  times 
that  shown  in  Table  XXII. 

TABLE  XXII 


Specimen. 

Name. 

Loss 
B.  T.  U. 
200  Lbs. 

Saving 
B.  T.  U. 

Saving  per 
Year  per 
100  Sq.  Ft. 

A.. 

Nonpareil  Cork  Standard.  . 

2   20 

11    64 

$37  80 

B... 

Nonpareil  Cork  Octagonal.  .  .  . 

2  38 

11    46 

37  20 

C.  .. 
D  
E  

Manville  Sectional,  H.  P  
Magnesia  
Imperial  Asbestos  

2.38 
2.45 
2  49 

11.46 
11.39 
11  35 

37.20 
36.90 
36  80 

F.  . 

W  B 

2  62 

11  2° 

36  40 

G  
H  

Asbestos  Air  Cell  
Manville  Infusorial  Earth 

2.77 
2  80 

11.07 
11*  04 

36.00 
35  85 

I.  •  .  .    . 

Manville  Low  Pressure 

2  87 

10  97 

35  65 

J  
K.  .  .     . 

Manville  Magnesia  Asbestos.  . 
Magnabestos 

2.88 
2  91 

10.96 
10  93 

35.60 
35  50 

L  

Moulded  Sectional 

3  00 

10  84 

35  20 

O  
P  

Asbestos  Fire  Board  
Calcite 

3.33 
3  61 

10  .  51 
10  23 

34.20 
33  24 

Bare  Pipe  

13.84 

0.00 

Inspection  of  Table  XXIV  shows  the  saving  due  to  the  use  of 
hair  felt  outside  of  a  standard  magnesia  cover. 

In  five  years  100  square  feet  of  hair  felt  saves  $7  more  than  its 
cost,  and  in  ten  years  it  saves  $20  above  its  cost. 

The  further  saving  due  to  a  second  inch  outside  the  first  is  $8 
in  ten  years.  Of  course  the  well-known  tendency  of  hair  felt  to 
deteriorate  should  be  considered. 

In  the  case  of  Nonpareil  Cork,  increasing  the  thickness  from  1  to 
2  inches  raises  the  cost  from  about  $25  to  $35  per  100  square  feet 
and  increases  the  net  saving  in  five  years  by  $10  and  by  $30  in  ten 
years.  In  other  words,  the  second  inch  of  material  in  use  about 
pays  for  itself  in  two  years,  while  the  first  pays  for  itself  in  about 
one  year.  The  third  inch  does  not  increase  the  saving  even  in  ten 
years.  The  second  inch,  therefore,  more  than  pays  for  interest 
and  depreciation,  while  the  third  fails  to  do  this. 

In  the  case  of  Asbestos  Fire  Board,  a  second  inch  in  thickness 
causes  a  saving  of  $20  in  ten  years,  the  third  and  fourth  inches 
showing  a  loss. 


BOILER  COVERINGS 


355 


In  general  it  may  be  said,  therefore,  that  if  five  years  is  the 
length  of  life  of  a  cover,  one  inch  is  the  most  economical  thickness, 
while  a  cover  which  has  a  life  of  ten  years  may  to  advantage  be 
made  2  inches  thick. 


TABLE  XXHI 

NET    SAVING    PER    100    SQ.    FT. 


Speci- 
men. 

Name. 

1  Year. 

2  Years. 

5  Years. 

10  Years. 

\ 

Nonpareil  Cork  Standard 

$12  80 

$50   60 

$164  00 

$353  00 

B... 

C  

Nonpareil  Cork  Octagonal  
Manville  Sectional  High  Pressure 

12.20 
12.20 

49.40 
49.40 

161.00 
161.00 

347.00 
347  00 

D 

Magnesia 

11  90 

48  80 

159  50 

344  00 

E 

Imperial  Asbestos  ...          .    . 

11  80 

48  60 

159  00 

343  00 

F 

W   B 

11  40 

47  80 

157  00 

339  00 

G 

Asbestos  Air  Cell 

11  00 

47  00 

155  00 

335  00 

H 

Manville  Infusorial  Earth.  .  . 

10  85 

46  70 

154  25 

333  00 

I  
J  
K 

Manville  Low  Pressure  
Manville  Magnesia  Asbestos.  .  .  . 
Magnabestos.  .  . 

10.65 
10.60 
10  50 

46.30 
46.20 
46  00 

153.75 
153.00 
152  50 

331.00 
331.00 
330  00 

L 

Watson's  Moulded  Sectional  .  . 

10  20 

45  40 

151  00 

327  00 

o 

Asbestos  Fire  Board  

9  20 

43  40 

146  00 

317  00 

P 

Calcite  

8  24 

41  48 

141  20 

307  00 

Q 

Bare  Pipe  

TABLE  XXIV 

VARIATIONS    IN    THICKNESS,    ETC. 


Specimen. 

Saving 
in 
B.  T.  U. 
per 
Sq.  Ft. 
per 
Minute. 

Saving 
in 
Dollars 
per  100 
Sq.  Ft. 
per 
Year. 

Net  Saving. 

-2 

J« 

s8 

Q. 

a 
< 

$30 
35 

40 

25 
35 

50 

25 
35 
50 
65 

1 
Year. 

2 
Years. 

5 
Years. 

10 
Years. 

Magnesia,     If      inches 
thick  

11.62 
12.38 

12.77 

11.64 
12.84 
12.94 

10.54 
11.48 
11.70 
11.83 

$37.75 
40.22 

41.50 

37.80 
41.75 
42.05 

34.20 
37.25 
38.00 
38.40 

$7.75 
5.22 

1.50 

12.80 
7.75 
7.95 

9.20 
2.25 
12.00 
26.60 

$45.50 
45.44 

43.00 

50.60 
48.50 
34.10 

43.40 
39.50 
26.00 
11.80 

$159 
166 

167 

164 
174 
160 

146 
151 
140 
127 

$347 
367 

375 

353 
383 
370 

317 
337 
330 
319 

Magnesia,     If     inches 
thick  and  1  inch  of 
hair  felt  
Magnesia,     If     inches 
thick  and  2  inches  of 
hair  felt  

Nonpareil  cork: 
1  inch  

2  inches  

Fire  board: 
1  inch 

2  inches     .    ... 

3  inches  

4  inches  

356 


STEAM-BOILERS 


TABLE  XXV 

LOSS  OF  HEAT  AT  200  POUNDS  FROM  BARE  PIPE 


Condition  of  Specimen. 

B.  T.  U.  Lost 
per  Sq.  Ft. 
per  Minute. 

New  pipe  

11.96 
13.84 
14.20 
13.85 
14.30 
12.02 
13.84 
13.90 
14.40 
12.10 

Fair  condition 

Rusty  and  black  

Cleaned  with  caustic  potash  inside  and  out  

Painted  dull  white  

Painted  gloss  v  white  

Cleaned  with  potash  again 

Coated  with  cylinder  oil 

Painted  dull  black  

Painted  glossy  black  

TABLE  XXVI 

VARIATION    OF    HEAT    LOSS    WITH    PRESSURE 


Pressure. 

Bare  Pipe. 
Loss  B.  T.  U.  perSq.  Ft. 
per  Minute. 

340 

15.97 

200 

13.84 

100 

8.92 

80 

8.04 

60 

7.00 

40 

5.74 

TABLE  XXVII 

MISCELLANEOUS    SUBSTANCES 


Specimen. 

B.  T.  U. 

per  Sq.  Ft. 
per  Minute 
at  200  Lbs. 

Saving  in 
One  Year  per 
100  Sq.  Ft. 
Pipe. 

Box  A. 
1  with  sand                                     

3  18 

$34  60 

2  with  cork    powdered  

1  75 

39  40 

3  with  cork  and  infusorial  earth  

1  90 

38  90 

4  with  sawdust      

2  15 

37  90 

5  with  charcoal  

2  00 

38  50 

6  with  ashes       

2  46 

36  90 

Brick  wall  4  inches  thick  

5  18 

28  80 

Pine  wood  1  inch        "    

3  56 

33  80 

Hair  felt     1     "          "    

2  51 

36  80 

Cabot's  seaweed  quilt  

2  78 

35  90 

Spruce  1  inch  thick  

3  40 

33  90 

"      2  inches  " 

2  31 

37  50 

(C            0           It                   (( 

2.02 

38.50 

Oak  1  inch  thick                      

3  65 

33  10 

Hard  pine  1  inch  thick     *. 

3  72 

32  90 

CARE  OF   BOILERS 


357 


The  box  A  referred  to  in  the  table  is  a  f-inch  pine  box,  large 
enough  to  surround  the  pipe  and  leave  a  1-inch  minimum  space  at 
its  four  sides. 

Table  XXVIII  is  a  comparison  of  results  obtained  by  D.  S. 
Jacobus  and  George  H.  Barrus  from  experiments  made  separately 
in  1901. 

TABLE  XXVIII 

AVERAGE  RESULTS  OBTAINED  FOR  2-INCH  PIPES  AS  MEASURED  BY  THE  PER- 
CENTAGE OF  THE  HEAT  RADIATED  BY  THE  BARE  PIPES  THAT  WAS  SAVED 
BY  APPLYING  THE  COVERINGS 


Covering. 

Tests  by 
Barrus. 

Tests  by 
Jacobus. 

Remanit  for  high-pressure  steam  

86  9 

Hair  Felt  

86  0 

Johns'  Asbesto-Sponge-Hair  Felt,  3-plv  

85   1 

Johns'  Asbesto-Sponge-Hair  Felt,  2-ply  
Asbesto-Sponge  Felted  (Sectional")  

84.4 
84  2 

84  9 

Remanit  for  low-pressure  steam  

84  4 

Keasbey  &  Mattison's  Magnesia  

S3  4 

83  2 

Johns'  Asbestos  Fire  Felt  (Navy  Brand) 

81   1 

82  3 

Johns'  Asbestocel 

76  3 

77  2 

New  York  Air  Cell 

75  9 

Carey's  Aloulded 

74  9 

John^'  Moulded 

74  8 

Cast's  Ambler  Air  Cell 

74  4 

74  4 

Johns'  Asbestos  Fire  Felt 

73  1 

It  may  be  well  to  explain  that  the  Johns'  Asbestos-Sponge- 
Hair  Felt  covering  is  made  up  of  layers  of  fabric  composed  of  fiber- 
ized  asbestos  and  carded  hair,  felted  and  laminated. 

Care  of  Boilers.  The  care  of  steam-boilers  is  all  important. 
They  are  often  sadly  neglected,  although  they  should  receive  as 
much  and  as  careful  attention  as  any  part  of  the  plant. 

A  boiler  should  be  so  designed  and  constructed  that  it  can  be 
inspected  at  all  parts,  and  the  owner  should  see  that  it  is  inspected 
by  some  competent  person.  A  boiler  which  cannot  be  so  inspected 
because  of  its  arrangement  or  setting  should  be  handled  with  cau- 
tion. 

All  internal  fittings,  as  fusible  plugs,  feed-pipes,  water-alarms, 
sediment-collectors,  and  the  like  should  be  examined  occasionally 
to  see  that  they  are  not  loose  an4  are  in  good  working  order.  In 
fact,  the  time  and  attention  given  to  a  steam-boiler  will  be  repaid 
many  fold  through  the  increase  in  its  life,  its  safety  and  its 
economy. 


358  STEAM-BOILERS 

At  periods  of  examination  and  cleaning  a  rigid  search  should 
be  made  for  corrosion  and  grooving,  both  externally  and  inter- 
nally. Corrosion  may  be  expected  anywhere,  but  points  especially 
liable  to  attack  are  at  the  water-line,  at  the  supports  and  at  places 
touched  by  brickwork  or  ashes.  Grooving  can  be  looked  for 
where  expansion  stresses  cause  a  bending  action,  as  at  lap-seams 
and  near  stay-ends. 

The  following  are  the  rules  for  management  and  care,  as  issued 
by  the  Hartford  Steam-boiler  Inspection  and  Insurance  Company: 

1.  Condition  of  Water. — The  first  duty  of  an  engineer,  when  he 
enters  his  boiler-room  in  the  morning,  is  to  ascertain  how  many 
gauges  of  water  there  are  in  his  boilers.     Never  unbank  nor  replen- 
ish   the  fires   until    this    is  done.      Accidents  have  occurred,  and 
many    boilers  have    been    entirely  ruined  from   neglect    of  this 
precaution. 

2.  Low  Water. — In  case  of  low  water,  immediately  cover  the 
fires  with  ashes,  or,  if  no  ashes  are  at  hand,  use  fresh  coal,  and  close 
ash-pit  doors.     Don't  turn  on  the  feed  under  any  circumstances, 
nor  tamper  with  or  open  the  safety-valve.     Let  the  steam  outlets 
remain  as  they  are. 

3.  In  Case  of  Foaming. — Close  throttle,  and  keep  closed  long 
enough  to  show  true  level  of  water.     If  that  level  is  sufficiently 
high,  feeding  and  blowing  will  usually  suffice  to  correct  the  evil. 
In  case  of  violent  foaming,  caused  by  dirty  water,  or  change  from 
salt  to  fresh  or  vice  versa,  in  addition  to  the  action  above  stated, 
check  draft  and  cover  fires  with  fresh  coal. 

4.  Leaks. — When  leaks  are  discovered  they  should  be  repaired 
as  soon  as  possible. 

5.  Blowing-off. — Clean  furnace  and  bridge  wall  of  all  coal  and 
ashes.     Allow  brickwork  to  cool  down  for  two  hours  at  least  before 
opening  blow.     A  pressure  exceeding  20  Ibs.  should  not  be  allowed 
when  boilers  are  blown  out.     Blow  out  at  least  once  in  two  weeks. 
In  case  the  feed  becomes  muddy,  blow  out  six  or  eight  inches  every 
day.     When  surface  blow-cocks  are  used,  they  should  be  often 
opened  for  a  few  moments  at  a  time. 

6.  Filling  Up  the  Boiler. — After  blowing  down  allow  the  boiler  to 
become  cool  before  filling  again.     Cold  water  pumped  into  hot  boil- 
ers is  very  injurious  from  sudden  contraction. 

7.  Exterior  of  Boiler. — Care  should  be  taken  that  no  water 


CAKE  OF   BOILERS  359 

comes  in  contact  with  the  exterior  of  the  boiler,  either  from  leaky 
joints  or  other  causes. 

8.  Removing   Deposit   and   Sediment. — In   tubular   boilers   the 
hand  holes  should  be  often  opened,  all  collections  removed,  and 
fire-plates  carefully  cleaned.     Also,  when  boilers  are  fed  in  front 
and  blown  off  through  the  same  pipe,  the  collection  of  mud  or 
sediment  in  the  rear  end  should  be  often  removed. 

9.  Safety-valves. — Raise   the  safety-valves  cautiously  and   fre- 
quently, as  they  are  liable  to  become  fast  in  their  seats  and  useless 
for  the  purpose  intended. 

10.  Safety-valve    and    pressure-gauge. — Should    the    gauge    at 
any  time  indicate  the  limit  of  pressure  allowed  by  this  company, 
see  that  the  safety-valves  are  blowing  off.     In  case  of  difference, 
notify  the  company's  inspector. 

11.  Gauge-cocks,  Glass  Gauge. — Keep  gauge-cocks  clear  and  in 
constant  use.     Glass  gauges  should  not  be  relied  on  altogether. 

12.  Blisters. — When  a  blister  appears  there,  must  be  no  delay 
in  having  it  carefully  examined   and   trimmed  or  patched,  as  the 
case  may  require. 

13.  Clean  Sheets. — Particular   care  should   be  taken  to   keep 
sheets  and  parts  of  boilers  exposed  to  the  fire  perfectly  clean,  also 
all  tubes,  flues  and  connections  well   swept.     This  is  particularly 
necessary  where  wood  or  soft  coal  is  used  for  fuel. 

14.  General  Care  of  Boilers  and  Connections. — Under  all  cir- 
cumstances keep  the  gauges,  cocks,  etc.,  clean  and  in  good  order, 
and  things  generally  in  and  about  the  engine  and  boiler-room  in  a 
neat  condition. 

15.  Getting   Up  Steam. — In  preparing  to  get  up  steam  after 
boilers  have  been  open  or  out  of  service,  great  care  should  be  exer- 
cised in  making  the  manhole  and  handhole  joints.      Safety-valve 
should  then  be  opened  and  blocked  open  and  the  necessary  supply 
of  water  run  in  or  pumped  into  the  boilers  until  it  shows  at  second 
gauge  in  tubular  and  locomotive  boilers ;  a  higher  level  is  advisable 
in  vertical  tubulars  as  a  protection  to  the  top  ends  of  tubes.     After 
this  is  done,  fuel  may  be  placed  upon  the  grate,  dampers  opened 
and  fires  started.     If  chimney  or  stack  is  cold  and  does  not  draw 
properly,  burn  some  oily  waste  or  light  kindlings  at  the  base. 
Start  fires  in  ample  time  so  it  will  not  be  necessary  to  urge  them 
unduly.      When    steam    issues    from    the    safety-valve,  lower    it 


360  STEAM-BOILERS 

carefully  to    its  seat  and  note  pressure   and  behavior   of  steam- 
gauge. 

If  there  are  other  boilers  in  operation  and  stop-valves  are  to  be 
opened  to  place  boilers  in  connection  with  others  on  a  steam  pipe 
line,  watch  those  recently  fired  up  until  pressure  is  up  to  that  of  the 
other  boilers  to  which  they  are  to  be  connected;  and,  when  that 
pressure  is  attained,  open  the  stop- valves  very  slowly  and  carefully. 


APPENDIX  A 

Superheated  Steam.*  When  steam  at  any  pressure  contains 
the  amount  of  heat  necessary  to  maintain  its  condition  as  the 
vapor  of  water,  it  contains  no  moisture,  and  is  said  to  be  "  saturated 
steam"  or  "dry  saturated  steam."  When  it  contains  moisture, 
it  is  said  to  be  "wet  steam."  In  the  latter  expression,  the  word 


FIG.  153. — Superheater  Attached  to  a  Babcock  and  Wilcox  Boiler. 

steam  means  the  apparent  evaporation,  since  the  wetness  con- 
tained is  not  steam,  but  finely  divided  particles  of  water  which  lack 
the  required  latent  heat. 

When  dry  saturated  steam  has  been  heated  to  a  temperature 
in  excess  of  the  boiling-point  corresponding  to  its  pressure,  it  is 
called  "  superheated  steam." 

The  object  of  using  superheated  steam  is  threefold:  It  acts 
more  nearly  as  a  perfect  gas ;  it  is  a  poorer  conductor  of  heat  than 


See  Trans.  American  Society  of  Mechanical  Engineers. 


361 


362 


STEAM-BOILERS 


wet  steam;  and  it  can  lose  heat  through  performance  of  work  and 
radiation  before  it  becomes  saturated  or  wet.    The  cylinder  con- 


FIG.  153a.— Section  of  Fig.  153. 

densation,  which  constitutes  one  of  the  chief  losses  of  heat  in  a 
working  engine,  is,  therefore,  greatly  reduced.     In  a  turbine,  the 


4*TUBE 


FIG.  154  — Foster's  Superheater  attached 
to  a  Fire-tube  Boiler. 


FJG.  154a.— Section  BB. 


reduction  in  steam  consumption  is  about  the  same  as  in  a  recipro- 
cating engine.  It  requires  less  heat  to  generate  superheated  steam 
than  it  does  dry  saturated  steam  at  the  same  temperature.  The 


APPENDIX   A 


363 


greatest  economies  are  reached  with  superheated  steam  in  simple- 
expansion  engines  and  in  engines  of  poor  design,  since  one  of  the 
objects  of  multiple  expansion,  steam  jackets,  reheaters,  and  similar 
complications  is  to  reduce  the  initial  condensation. 

Experience  has  shown  that  the  comparative  economy  of  super- 
heated over  saturated  steam  diminishes  rapidly  beyond  the  point 
of  double  expansion.  There  is  less  advantage  in  using  superheated 
steam  in  triple-  or  quadruple-expansion  engines  unless  some  gains 


FIG.  155  —Detail  of  Return  Header  and  Elements. 

Portion  of  Foster  Superheater  showing  ends  of  elements  connected  by  return  header. 
The  elements  consist  of  seamless  drawn  steel  tubing  protected  by  cast-iron  rings  shrunk 
on.  Inner  tubes  are  closed  to  steam,  which  is  thus  forced  through  thin  annular  spaces  and 
rapidly  superheated. 

are  sought  other  than  a  lessening  of  cylinder  or  initial  condensa- 
tion. 

The  economy  derived  by  the  proper  use  of  superheated  steam 
appears  to  vary  according  to  conditions  from  nothing  to  40  per 
centum  of  the  fuel  required.  The  maximum  saving  is  found  in 
slow-moving,  simple  engines,  such  as  direct-acting  pumps.  It  also 
appears  when  superheated  steam  is  used  that  the  weight  of  steam 


364 


STEAM-BOILERS 


consumed  by  an  engine  per  unit  of  power  becomes  nearly  uniform, 
and  is  therefore  less  dependent  on  the  size  of  the  engine. 

The  use  of  superheated  steam  is  based  on  correct  thermody- 
namic  principles.  The  plant  is  complicated  by  the  superheater, 
and  the  operating  costs  are  increased  by  radiation  losses,  re- 
pairs, renewals  to  both  engine  and  heater,  interest  and  de- 
preciation. The  engine  is  subject  to  a  change  of  form  due  to 
uneven  expansion  with  high  temperatures,  and  consequently 


HERRINGBONE  GRATES.  ^  AIR 
SPACES.    INCLINATION  &">ER  FT. 


SECTION  C-C. 


FIG.  156. — Foster's  Superheater — Direct-fired  type. 

greater  care  must  be  exercised  in  the  design  of  its  parts.  The  effect 
of  introducing  superheat  may  simplify  a  plant  by  the  elimination 
of  other  features.  The  specific  heat  of  steam  was  determined  by 
Regnault  to  be  0.48.  Recent  experiments  show  that  it  increases 
with  the  pressure  and  temperature;  thus,  at  150  pounds  the  specific 
heat  is  about  0.55.  Superheated  steam  will  lose  heat  as  readily  as 
it  will  receive  it,  which  makes  it  essential  that  pipes  and  surfaces 
be  well  covered. 

The  greatest  benefit  with  the  least  complication  is  obtained  with 
steam  heated  to  a  temperature  not  in  excess  of  550°  Fahr.  at  the 


APPENDIX  A 


365 


engine;  and  with  pressures  of  about  160  pounds  per  square  inch. 
The  amount  of  superheating  surface  required  is  difficult  to  deter- 
mine in  advance.  Practically  it  varies  from  about  10%  to  100% 
of  water-heating  surface.  The  surface  is  made  up  of  tubes  of 
wrought-iron  or  steel.  Wrought-iron  and  steel  tubes  seldom  show 
pitting  or  corrosion,  but  must  have  a  circulation  through  them  or 
they  will  burn  out.  When  not  fitted  with  a  cast-iron  protecting 


HALF  SECTION  A-A. 


HALF  SECTION  B-B. 


FIG.  1560.— Sections  of  Fig.  156. 

cover,  superheaters  should  be  arranged  to  be  flooded  when  not  in 
use,  and  the  water  must  be  drained  off  before  the  circulation  can  be 
re-established.  Screw  joints  should  be  avoided,  but  if  they  have  to 
be  used  the  threads  should  be  cut  as  perfectly  as  possible  and  the 
joints  made  with  a  paste  of  plumbago  mixed  with  linseed  oil.  Ex- 
panded ends  are  better  than  screw- joints  when  possible.  The  tubes 
are  1J  inches,  2  inches,  or  4  inches  in  diameter. 


366  STEAM-BOILERS 

Superheaters  fitted  with  cast-iron  covers  have  an  advantage  due 
to  the  reserve  of  heat  stored  in  the  greater  weight  of  metal,  and  the 
surface  should  be  ribbed  or  fluted  on  the  outside. 

The  cost  of  superheating  surface  is  nearly  the  same  as  that  for 
an  equal  amount  of  boiler-heating  surface. 

Figs.  153  and  153a  illustrate  a  superheater  attached  to  a  water- 
tubular  boiler  of  the  Babcock  &  Wilcox  design.  Figs.  154  and  154a 
illustrate  E.  H,  Foster's  superheater  attached  to  a  fire-tube  boiler. 

Fig.  155  illustrates  Foster's  detail  of  return  header  protected 
by  cast-iron  rings.  Figs.  156  and  156a  illustrate  Foster's  direct- 
fired  type  of  superheater. 


APPENDIX  B 

FAN  WHEEL  WITH  PERIPHERAL  DISCHARGE 

CALCULATIONS   FOR    CAPACITY,    REVOLUTIONS,    AND    BRAKE    HORSE- 
POWER 


o        y2         i        \y2        2         zj£        3 

PRESSURE  IN  OUNCES  PkH  SQUAKE  INCH. 

0      |      If      2|      8*      4f     5£     6i      7 

PRBBSURIC  IN  INCHES  OF  WATER. 

Q=  Air  discharged  in  cu.  ft.  per  minute. 
d= diameter  of  wheel  in  feet. 
w= width  of  wheel  at  tip  of  blades  in  feet. 
R  =  re  volutions  per  minute. 

V= peripheral  velocity  of  wheel  in  feet  per  minute. 
1;'=  theoretical  velocity  of  air      "     "      "        " 
v=  actual  velocity  of  air  "     "      "        " 

D= density  of  air  in  pounds. 
P=  brake  h.  p.  to  drive  wheel. 

a=effective  area  of  discharge  or  "  blast  area"  in  square  feet. 
Width  of  blades  at  tip  is  usually  made  about  0.4 Xd. 
Width  of  blades  at  widest  part  is  made  about  0.5 Xd. 

367 


368 


STEAM-BOILERS 


*  When  small  volume  of  air,  discharged  at  high  pressure,  is  desired, 

the  width  is  less. 

*  When  large  volume  of  air,  discharged  at  low  pressure,  is  desired, 

the  width  is  greater. 

a—Q-^-V.     By  experiment,  approximately  a  =wd  +  3.      Therefore 
a=0.4d2-f-3,  from  which  d  can  be  found. 


Inlet  area  in  sq.  ft.=0.00054Q-^v  water  pressure  in  inches,  but 
should  not  exceed  40  per  cent  of  disc  area 
of  side  of  wheel. 
Outlet  area  in  sq.  ft.  =  constant  X  inlet  area. 

For  free  discharge,  constant  varies  from 

1.0  to  1.25. 

For  restricted  discharge,  as  into  ducts,  the 
fan  should  be  calculated  for  a  pressure 
equal  to  that  at  outlet  plus  friction. 

Q  X  D  X  v'2 

Theoretical  b.  h.  p.  to  drive  fan  wheel  =  -^—-  —  —  ;  Q  and  v'  being 

oou  X  £(j 

taken  in  feet  per  second  and  Q  =  aXV. 

.'.  P=theo.  h.  p.X2.  The  efficiency  being  taken  at  50  per  cent. 

VALUES  OF  K  FOR  VARYING  TEMPERATURES. 


30° 

F.  =  098 

200°  1 

*.-1.14 

400°  F. 

=  1.30 

50° 

=  1.00 

250° 

=  1.18 

450° 

=  134 

100° 

=  1.05 

300° 

=  1.22 

500° 

=  1.37 

150° 

=  1.09 

350° 

=  1.26 

550° 

=  1.41 

At  any  temperature  F.,  the  velocities  =KX velocity  at  50°  F. 
Therefore,  work  out  fan  problem  with  corrected  velocities  cor- 
responding to  the  temperature. 


*  This  is  true  when  d  or  R  is  fixed,  and  V  or  discharge  pressure  is  known. 
Usual  Max.  for  F=6600  ft.  per  min.,  but  should  not  exceed  7200  ft.permin. 


SATURATED-STEA.M   TABLES. 


fij 

14- 

2 
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1  . 

1 

11 

«  g' 

ll 

ill 

3 

1 

1 

t-    03 

^    fi4  DO 

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H  -* 

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3 

li 

2  Js 

?-   3  1o 

"3 

"5 

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SB 

wl 

K8 

11 

* 

p 

h 

H 

L 

E 

I  =  H-E 

WJ 

v 

fo 

102-0 

70-0 

1113-1 

1043-0 

98PM 

61-9 

1051-2 

0-00299 

334-6 

2-0 

126-3 

94-4 

1120-5 

1026-1 

961-9 

64-2 

1056-3 

0-00576 

173-6 

3-0 

1416 

109-8 

1125-1 

1015-3 

949-5 

65-8 

1059-3 

0-00844 

1184 

4-0 

1531 

1214 

1128-6 

1007-2 

9404 

66-8 

1061-8 

0-01107 

9031 

5-0 

162-3 

130-7 

1131-5 

1000-8 

933-1 

677 

1063-8 

0-01366 

73-22 

6-0 

170-1 

138-6 

1133-8 

995-2 

926-7 

68-5 

1065-3 

0-01622 

61-67 

70 

176-9 

145-4 

1135-9 

990-5 

9214 

69-1 

1066-8 

0-01874 

5337 

8-0 

182-9 

151-5 

1137-7 

986-2 

916-5 

69-7 

1068-0 

002112 

47-07 

9-0 

188-3 

156-9 

1139-4 

982-5 

912-4 

70-1 

1069-3 

0-02374 

42-13 

10-0 

193-2 

161-9 

1140-9 

979-0 

908-4 

706 

1070-3 

0-02621 

3816 

11-0 

197-8 

166-5 

1142-3 

975-8 

904-8 

71-0 

10713 

0-02866 

34-88 

12-0 

202-0 

170-7 

11436 

972-9 

901-5 

71-4 

1072-2 

0-03111 

32-14 

13-0 

205-9 

174-6 

1144-7 

970-1 

898-4 

71-7 

1073-0 

0-03355 

29-82 

14-0 

2096 

178-3 

1145-8 

967-5 

895-5 

72-0 

1073-8 

0-03600 

27-79 

147 

212-0 

180-7 

1146-6 

965-8 

893-5 

72-3 

1074-2 

0-03758 

26-64 

15-0 

2130 

181-8 

1146-9 

965-1 

892-6 

72-5 

1074-4 

0-03826 

2615 

160 

216-3 

185-1 

1147-9 

962-8 

890-0 

728 

1075-1 

0-04067 

24-59 

17-0 

219-4 

188-3 

11489 

960-6 

887-6 

73-0 

1075-9 

0  04307 

2322 

18-0 

222-4 

191-3 

1149-8 

958-5 

885-3 

73-2 

1076-6 

0-04547 

22-00 

19-0 

225-2 

194-1 

1150-7 

956-6 

883-2 

73-4 

1077-3 

0-04786 

20-90 

20-0 

227-9 

196-9 

1151-5 

954-6 

881-0 

73-6 

1077-9 

0-05023 

1991 

21-0 

230-5 

199-5 

11523 

952-8 

879-0 

73-8 

1078-5 

0-05259 

19-01 

22-0 

233-1 

202-0 

1153-0 

951-0 

877-0 

74-0 

1079-0 

0-05495 

18-20 

230 

2355 

204-5 

1153-7 

949-2 

875-0 

74-2 

1079-5 

0-05731 

17-45 

24-0 

237-8 

206-8 

11544 

947-6 

873-2 

74-4 

1080-0 

0-05966 

1676 

25-0 

240-0 

209-1 

1155-1 

9460 

871-5 

74-5 

1080-6 

0-06199 

16-13 

26-0 

242-2 

211-2 

1155-8 

944-6 

8699 

74-7 

1081-1 

0-06432 

15-55 

27-0 

244-3 

213-4 

1156-5 

943-1 

868-2 

74-9 

1081-6 

0-06666 

15-00 

These  Tables  are  reproduced  from  "  Steam  Engine  Theory  and  Practice/' 
by  William  Ripper,  M.I.C.E.,  and  are  for  the  most  part  taken  from  Professor 
Peabody's  valuable  "Saturated  Steam  Tables,"  by  kind  permission  of  the 
author  and  publishers  (Messrs.  John  Wiley  and  Sons,  New  York). 


370 


SATURATED-STEAM  TABLES— Continued. 


11 

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28-0 

t 

246-4 

h 
215-4 

H 

1157-1 

L 
941-7 

86<3-7 

E 
75-0 

1082-1 

0-06899 

V 
14-49 

290 

248-3 

2174 

1157-7 

940-3 

865-1 

75-2 

1082-5 

0-07130 

14-03 

30-0 

250-3 

219-4 

1158-3 

938-9 

863-6 

753 

1083-0 

0-07360 

13-59 

31-0 

252-1 

221-3 

1158-8 

937-5 

862-0 

75-5 

1083-3 

0-07590 

13-18 

32-0 

254-0 

223-1 

1159-4 

936-3 

860-7 

756 

1083-8 

0-0782  L 

12-78 

33-0 

255-8 

224-9 

11599 

935-0 

859-2 

75-8 

1084-1 

0-08051 

1241 

34-0 

257-5 

226-7 

1160-4 

933-7 

857-8 

75-9 

1084-5 

0-08280 

12-07 

35-0 

259-2 

228-4 

1161-0 

932-6 

856-6 

76-0 

1085-0 

0-08508 

11-75 

40-0 

267-1 

236-4 

1163-4 

927-0 

850-3 

76-7 

1086-7 

0-09644 

10-37 

45-0 

274-3 

243-6 

1165-6 

922-0 

844-8 

77-2 

1088-4 

0-1077 

9-287 

50-0 

280-8 

250-2 

1167-6 

917-4 

839-7 

77-7 

1089-9 

0-1188 

8-414 

55-0 

286-9 

256-3 

1169-4 

913-1 

834-9 

78-2 

1091-2 

0-1299 

7-696 

60-0 

292-5 

261-9 

1171-2 

909-3 

830-7 

78-6 

1092-6 

0-1409 

7-096 

65-0 

297-8 

267-2 

1172-7 

905-5 

826-5 

79-0 

1093-7 

0-1519 

6-583 

70-0 

302-7 

272-2 

11743 

902-1 

822-7 

79-4 

1094-9 

0-1628 

6-144 

75-0 

307-4 

276-9 

1175-7 

898-8 

819-1 

79-7 

1096-0 

01736 

5-762 

80-0 

311-8 

281-4 

1177-0 

895-6 

815-5 

801 

1096-9 

01843 

5425 

85-0 

316-0 

285-8 

1178-3 

892-5 

812-1 

80-4 

1097-9 

0-1951 

5-125 

90-0 

3200 

290-0 

1179-6 

889-6 

808-9 

80-7 

10989 

0-2058 

4-858 

.95-0 

323-9 

294-0 

1180-7 

886-7 

805-8 

80-9 

1099-8 

0-2165 

4-619 

100-0 

327-6 

297-9 

11819 

884-0 

802-8 

81-2 

1100-7 

0-2271 

4-403 

105-0 

331-1 

301-6 

1182-9 

881-3 

799-9 

81-4 

1101-5 

0-2378 

4-206 

110-0 

3346 

305-2 

1184-0 

878-8 

7971 

81-7 

1102-3 

0-2484 

4-026 

1150 

337-9 

308-7 

1185-0 

876-3 

794-4 

81-9 

1103-1 

0-2589 

3-862 

120-0 

341-0 

312-0 

1186-0 

874-0 

791-9 

82-1 

11039 

0-2695 

3-711 

1250 

344-1 

3152 

1186-9 

871-7 

789-4 

82-3 

1104-6 

0-2800 

3-572 

130-0 

347-1 

3184 

1187-8 

869-4 

786-9 

82-5 

1105-3 

0-2904 

3-444 

135-0 

350-0 

321-4 

1188-7 

867-3 

784-7 

82-6 

1106-1 

0-3009 

3-323 

140-0 

352-8 

324-4 

1189-5 

865-1 

782-3 

82-8 

1106-7 

03113 

3-212 

145-U 

355-6 

327-2 

1190-4 

863-2 

780-2 

83-0 

1107-4 

0-3218 

3-107 

150-0 

358-3 

330-0 

11912 

861-2 

778-1 

83-1 

1108-1 

0-3321 

3-011 

f  155-0 

360-9 

332-7 

1192-0 

859-3 

776-0 

83-3 

1108-7 

0-3426 

2-919 

160-0 

363-4 

335-4 

1192-8 

857-4 

774-0 

83-4 

1109-4 

03530 

2-833 

165-0 

365-9 

33S.O 

1193-6 

855-6 

772-0 

83-6 

1110-0 

0-3635 

2-751 

170-0 

368-3 

34d5 

1194-3 

853-8 

770-1 

83-7 

1110-6 

03737 

2-676 

175-0 

370-6 

343-0 

1195-0 

852-0 

768-2 

83-8 

1111-2 

0-3841 

2-603 

180-0 

373-0 

345-4 

11957 

850-3 

766-4 

83-9 

1111-8 

03945 

2-535 

185-0 

375-23 

3478 

1196-4 

848-6 

764-6 

84-0 

1112-4 

0-4049 

2-470 

190-0 

377-4 

350-1 

1197-1 

847-0 

762-9 

84-1 

11130 

0-4153 

2-408 

195-0 

379-6 

352-4 

1197-7 

845-3 

761-1 

84-2 

11135 

0-4257 

2-349 

200-0 

381-7 

354-6 

1198-4 

843-8 

759-5 

84-3 

1114-1 

0-4359 

2-294 

250-0 

401-0 

374-7     1204-2 

829-5 

744-5 

85-0 

1119-2 

0-5393 

1-854 

300-0 

417-4 

391-9  i  1209-3 

817-4 

732-0 

85-4 

1123-9 

0-6440 

1-554 

400-0 

444-9 

419-8     1217-7 

797-9 

712-3 

86-2 

1131-5 

0-8572 

1-167 

INDEX 


Absolute  Zero,  4. 

Adamson  Ring,  174. 

Admiralty  Boiler,  100. 

Advantages  of  Oil  Fuel,  53. 

Advantages  of  Water-tubular  Boil- 
ers, 111. 

Air  for  Combustion,  Calculation  of, 
26,  349. 

Air,  Quantity  of — for  Combustion, 
23,  349 

Air-supply,  14, 16,  278,  280,  338,  342. 

Air-supply,  Heating  of,  59. 

Alarms,  Water,  274. 

Almy  Boiler,  113. 

Analyses  of  Boiler  Scale,  312. 

Analyses  of  Fuel  Oils,  51. 

Analyses  of  Gases  of  Combustion,  21. 

Analysis  of  Powder  in  Pits,  321. 

Anthracite,  32. 

Area  for  Draft,  132,  2SO. 

Area  of  Chimney,  135. 

Area  of  Steam-pipe,  122. 

Artificial  Draft,  127,  300. 

Ash,  22,42,347. 

Ash-pit,  285. 

Atmospheric  Air,  17. 

Atomizing,  Liquid  Fuel,  43. 

Avogadro,  Laws  of,  20. 

Babcock  &  Wilcox  Boiler,  113. 
Back  Connection,  206. 
Bagasse,  37. 
Belleville  Boiler,  113. 
Best  Boiler,  63. 
"Best"  Draft,  129. 


Bituminous  Caking  Coal,  33. 

Bituminous  Coal,  33. 

Bituminous  Portion  of  Coal,  16. 

Blisters,  321,  359. 

Blow-offs,  79,  265. 

Blowing  Off,  313,  35S. 

Bodies — Solid,    Fluid,    Liquid,    Gas- 
eous, 1. 

Boiler  Coverings,  350. 

Boiler  Efficiency,  60. 

Boiler  Feed,  251. 

Boiler  Proportioning  for  a  Required 
Duty,  115. 

Boiler  Testing,  345. 

Boiler  Trials,  346. 

Boiler    Trials,    Calculation    of    Re- 
sults, 346. 

Boilers,  Classification  of,  63. 

Boilers,  Horse-power  of,  63. 

Boiling,  10. 

Bowling  Hoop,  173. 

Boyles'  Law,  2. 

Brass,  152. 

Brazing,  150,  152. 

Breeching,  136,  286. 

Brick  Stacks,  330. 

Bridge  Wall,  228. 

Bridge  Wall,  Split,  229,  278. 

Bridge  Wall,  Wet,  103. 

Brine,  10,  294. 

British  Thermal  Unit,  4. 

Bronze,  152. 

Brown  Coal,  34. 

Bursting  Pressure,  155. 

Buying  Coals,  35. 

371 


372 


INDEX 


Calking,  213,  215,  321. 

Calculation  of  Riveted  Joint,  218. 

Calorimeters  for  Measuring  Moist- 
ure, 347. 

Carbon,  Air  Required  to  Burn,  24, 
349. 

Carbon,  Anhydride,  13. 

Carbon  Dioxide,  13,  17. 

Carbon  Monoxide,  14,  17,  19. 

Care  of  Boilers,  323,  357. 

Cast  Iron,  138. 

Cast  Steel,  148. 

Charcoal,  37. 

Charcoal-iron  Boiler- tubes,  141. 

Charles'  Law,  2. 

Chimney  Design,  327. 

Chimney  Draft,  125. 

Chimneys,  Separate,  for  Boilers,  328. 

Classification  of  Boilers,  63. 

Classification  of  Fuels,  32. 

Closed  Ash-pit  for  Artificial  Draft, 
304,  307. 

Closed  Fire-room  for  Artificial  Draft, 
307. 

Coal,  31. 

Coal  Gas,  16,  17. 

Coal,  Size  of,  34. 

Coals,  Composition  of,  40. 

Coals,  When  Buying,  35. 

Coburn  Safety-valve,  269. 

Cocks,  Try,  273,  275. 

Coke,  37. 

Color  Test  for  Temperature,  56. 

Collapsing  Pressure,  157,  170. 

Combustible,  22,  60,  346. 

Combustion,  13,  18. 

Combustion-chamber,  205. 

Combustion  of  Coal,  15. 

Combustion,  Heat  of,  29. 

Combustion,  Products  of,  21. 

Combustion,  Rate  of,  131,  132,  347. 

Combustion,  Requirements  for  Per- 
fect, 21,  337. 

Combustion,  Volume  of  Air  Required 
for,  25. 

Compound  Boiler,  105. 

Conduction  of  Heat,  2. 


Contraction,  226,  323. 
Convection  of  Heat,  2. 
Copper,  150,  239. 
Copper  Fire-boxes,  105. 
Cornish  Boiler,  85. 
Corrugated  Furnace,  65,  175. 
Corrosion,  216,  218,  319,  322. 
Coverings  of  Boilers  and  Pipes,  350* 
Culm,  35. 

Dalton's  Law,  2. 

Dead  Plate,  281,  343. 

Densities  of  Gases,  6. 

Deposit  in  Boiler,  359. 

Design  of  Boilers,  68. 

Design  of  Steam-piping,  247. 

Disadvantages     of     Water  -  tubular 

Boilers,  111. 
Dissipation  of  Heat  in  the  Furnace, 

58. 
Distance  between  Grate  and   Boiler, 

278,  338. 
Domes,  232. 

Down-draft  Grate,  284,  338,  343. 
Draft  Area,  135. 
Draft  of  Chimney,  125,  132. 
Draft  Regulator,  2S6. 
Draft,  Split  and  Wheel,  87. 
Drips,  250. 
Drum,  Steam,  234. 
Drum-boiler,  90. 
Dry  Bituminous  Coal,  33. 
Dry  Pipe,  250. 
Dry  Saturated  Steam,  361. 
Dry  Steam,  Commercially,  122. 
Duplicate  System   of   Steam-piping, 

241. 

Economizer,  260. 

Efficiency  of  Boiler  and  Grate,  60. 
Efficiency  of  Furnace,  58. 
Equivalent  Evaporation,  11,  347. 
Evaporation,  Factor  of,  11. 
Evaporation,  Rate  of,  60. 
Evaporation,  Total  Heat  of,  9. 
Evaporative  Power  of  a  Fuel,  11. 
Evaporators,  293. 


INDEX 


373 


Excess  of  Air,  16,  18 
Expanders  for  Tubes,  190. 
Expansion,  241,  323. 
Explosions,  324. 
External  Corrosion,  322. 

Factor  of  Evaporation,  11. 

Factor  of  Safety,  157. 

Failures  of  Riveted  Joints,  218. 

Failures  of  Steam-pipes,  238. 

Fans  for  Draft,  127,  129,  304. 

Feed,  99,  251. 

Feed-pumps,  256. 

Feed-water  Heaters,  257. 

Ferrules  for  Tube  Ends,  192,  308. 

Filters,  264,  317. 

Fire-doors,  2  6. 

Firemen  per  Horse-power,  54. 

Fire-tubular  Boilers,  63. 

Fittings,  139,  231. 

Flame,  16. 

Flanges,  244. 

Flat  Surfaces,  164. 

Flue  and  Return-tubular  Boiler,  84. 

Flues,  170. 

Flues,  Methods  of  Strengthening,  172. 

Foaming,  122,  358. 

Forced  Draft,  300. 

Foundations  for  Stacks,  328. 

Fox's  Corrugated  Furnace,  175. 

Fresh  Charge  of  Coal  on  a  Fire,  14, 16. 

Fuel  Classification,  32. 

Fuel,  31,  60. 

Fuel,  Heating  Power  of,  29. 

Fuel  Ratio,  32. 

Fuels,  Principal,  13. 

Fuels,  Protection  from  Weather,  40. 

Fur,  310. 

Furnace  Temperature,  56. 

Fusible  Plug,  272. 

Galloway  Boiler,  88. 
Galloway  Tubes,  85,  88,  174. 
Galvanic  Action,  251,  267,  316,  322. 
Gas,  Perfect,  1. 
Gaseous  Fuels,  53. 
Gases,  Laws  of,  2. 


Gases  from  Combustion,  21. 

Gaskets,  232. 

Gauge,  Steam,  272,  359. 

Gauge,  Water,  273,  359. 

Gay-Lussac's  Law,  2. 

Generator,  Steam,  62. 

Girders,  205. 

Grate,  Distance  from,  to  Boiler,  278, 

338. 

Grate,  Height  from  Floor,  279 
Grates,  278,  338. 
Grooving,  213,  216,  321,  323. 
Gruner's  Classification  of  Fuel,  32. 
Gunboat  Boiler,  100. 
Gusset  Plates,  198. 
Guys  for  Stacks,  328. 

Handholes,  275. 

Heads,  Boiler,  162. 

Heat,  2. 

Heat  Applied  to  Coal,  15. 

Heat  Balance,  50,  350. 

Heat  Dissipated  in  a  Furnace,  58. 

Heat  of  Combustion,  29,  41,  43. 

Heat  of  Combustion  of  Gases,  55. 

Heat  of  Combustion  of  Oils,  43. 

Heat  to  Evaporate  Moisture,  42, 

Heat  Utilized,  58. 

Heaters,  Feed-water,  257. 

Heating  Power  of  a  Fuel,  29,  40,  51, 

54. 

Heating  Surface,  65. 
Height  of  Chimney,  133,  135,  328. 
Horizontal  Return-tubular  Boiler,  71. 
Horse-power  of  Boilers,  63,  348. 
Horse-power  of  Chimney,  135. 
Huston  Stay,  201. 
Hydrocarbon  Portion  of  Coal,  16. 
Hydrogen,  Air  Required  to  Burn,  24. 
Hydrokineter,  99. 

Idle  Boilers,  Care  of,  323. 
Incrustation,  310. 
Induced  Draft,  300,  308. 
Injectors  or  Inspirators,  254. 
Internal  Corrosion,  319,  321. 
Internal  Pipe,  250. 


374 


INDEX 


Jet  for  Draft  in  Stack,  127,  129,  300, 

302. 
Jet  for  Draft  under  Grate,  28,  304, 

342. 

Kent's  Classification  of  Coals,  32. 

Ladders  on  Stacks,  331. 
Lancashire  Boiler,  87. 
Latent  Heat,  6. 

Latent  Heat  of  Evaporation,  7. 
Latent  Heat  of  Expansion,  8. 
Latent  Heat  of  Fusion,  7. 
Laws  of  Avogadro,  20. 
Laws  of  Gases,  2. 
Lightning-rods  on  Stacks,  331. 
Lignite,  34. 
Linings,  183,  236. 
Liquid  Fuels,  42. 

Liquid  Fuels,  Advantages  and  Dis- 
advantages of,  53. 
Locomotive  Boiler,  103. 
Long-flaming  Bituminous  Coal,  33. 
Losses  Due  to  Smoke,  15,  336. 
Low  Water,  358. 
Lugs,  65. 

Malleable  Cast  Iron,  138. 
Manholes,  275. 
Manning  Boiler,  82. 
Marine  Boiler,  100. 
Mariotte's  Law,  2. 
Marsh  Gas,  17,  23. 
Materials,  138,  238. 
Mechanical  Draft,  300. 
Mechanical  Equivalent  of  Heat,  3. 
Mechanical  Stokers,  295,  338,  343. 
Methods  of  Firing,  27,  338,  342. 
Moisture,  Heat  Required  to  Evapo- 
rate, 42. 

Moisture  in  Steam,  122,  348. 
Morison  Furnace,  65,  175. 
Mud  Drums,  265. 
Muntz  Metal,  152,  153. 

Natural  Draft,  127,  130. 
Naval  Brass,  153. 


Nickel-steel,  148,  188. 
Nickel-steel  Rivets,  147. 
Niclausse  Boiler,  113. 
Nuts  for  Stays,  197,  202. 

Object  of  Using  Superheated  Steam, 
361. 

Oil  Burners,  43,  52. 

Oil  Fuel,  Advantages  and  Disad- 
vantages of,  53,  192. 

Oil  Fuel  Compared  to  Coal,  52. 

Oils,  Composition  of  Fuel,  51. 

Olefiant  Gas,  17,  24. 

Orsat  Gas  Apparatus,  21. 

Peat,  36. 

Perfect  Combustion,  Requirements 

of,  21,  337. 
Perfect  Gas,  1. 
Petroleum  Oils,  42. 
Pipe  Coverings,  350. 
Pitch  for  Rivets,  213,  221,  223. 
Pitting,  320. 

Plain  Cylindrical  Boiler,  70. 
Pressure,  Bursting,  155. 
Pressure,  Collapsing,  157,  170. 
Priming,  10,  111,  121,  187,  358. 
Priming,  Calorimeters  for  Measuring, 

347. 

Products  of  Combustion,  21. 
Proportion  of   Boiler  to   Perform  a 

Required  Duty,  115. 
Proportion  of  Riveted  Joint,  223. 
Protection  from  Weather  of  Fuels,  40. 
Pulverizing,  Liquid  Fuel,  43. 
Purves'  Furnace,  63,  175. 
Pumps,  Feed,  256. 

Quantity  of  Air  for  Combustion,  23, 
349. 

Radiation  of  Heat,  2. 
Rankine's  Classification  of  Coals,  32. 
Rate  of  Combustion,  131,  132,  347. 
Rate  of  Evaporation,  60. 
Ratio  of  Heating  to  Grate  Surface, 
66,  67. 


INDEX 


375 


Refuse,  22,  346. 
Reinforcing  Steam-pipes,  239. 
Relative  Volume  of  Steam,  11. 
Requirements   for   Perfect   Combus- 
tion, 21. 
Retarders,  192. 
Return  Trap,  289. 
Ringlemann's  Smoke-scales,  339. 
Rivet-holes,  216. 
Rivet-iron,  141. 
Rivet-steel,  142,  146. 
Rivet  Strength,  214. 
Riveting,  207. 
Riveting,  Power,  214. 
Rivets,  Countersunk,  211. 
Rivets,  Pressure  on,  214. 
Rules  for  Corrugated  Furnaces,  180. 
Rules  for  Flat  Surfaces,  165. 
Rules  for  Flues,  177. 
Rules  for  Linings,  183. 
Rules  for  Ribbed  Flues,  181. 
Rules  for  Stays,  203. 
Rules  for  Thickness  of  Heads,  164. 
Rules  for  Thickness  of  Shell,  157. 
Rules  for  Tubes,  180,  194. 

Safety-valves,  269,  359. 

Salt  Water,  10,  294. 

Saturated  Steam,  361. 

Sawdust,  37,  284. 

Scale,  Boiler,  310,  359. 

Scale,  Prevention,  313. 

Scotch  Boiler,  90. 

Sediment,  359. 

Semi-anthracite,  33. 

Semi-bituminous  Coal,  33. 

Sensible  Heat,  1. 

Separators,  292. 

Serve  Tube,  65,  194. 

Setting,  Boiler,  75,  226. 

Setting,  Boiler,  to  Prevent  Corro- 
sion, 322. 

Shaking  Grates,  283. 

Shell,  Boiler,  154,  160. 

Shell,  Maximum  and  Minimum 
Thickness,  160. 

Shell,  Rules  for  Thickness,  157. 


Shell,  Strength  Due  Ends,  156. 
Size  of  Coals,  34. 
Sludge,  310. 
Smoke,  14,  336. 
Smoke-connection,  286. 
Smoke-consumers,  15. 
Smoke,  Losses  Due  to,  15,  336. 
Smoke  Prevention,  14,  336,  342. 
Smoke  -  scales,    Prof.    Ringlemann's, 

339. 

Soda,  314. 
Specifications    for    Boiler-plate  and 

Shapes,  143. 
Specifications      for      Charcoal  -  iron 

Boiler-tubes,  141. 
Specifications     for    Rivet-rods    and 

Finished  Rivets,  146. 
Specifications  for  Rods,  Shapes,  and 

Forgings,  144. 
Specific  Heat,  4. 
Specific  Volume  of  Steam,  11. 
Split  Bridge  Wall,  229,  278. 
Stacks,  327. 

Stacks,  Separate,  for  Boilers,  328. 
Stacks,  Stability  of,  328. 
Stacks,  Steel,  332. 
Stay-tubes,  191. 
Stays,  194. 

Stays,  Nuts  for,  197,  202. 
Stays,  Telltale  in,  196. 
Steam-chimney,  101,  236. 
Steam,  Commercially  Dry,  122. 
Steam-dome,  232. 
Steam-drum,  101,  234. 
Steam-gauge,  272. 
Steam  Jets,  28,  128,  301,  302,  304, 

342. 

Steam-pipes,  138,  152,  237. 
Steam-pipes,  Area  of,  122. 
Steam-pipes,  Failures  of,  238. 
Steam-pipes,  Flanges  of,  244. 
Steam-pipes,  Materials,  238. 
Steam-space,  120,  122. 
Steam-superheater,  101,  235,  361. 
Steel,  142. 
Stirling  Boiler,  113. 
Stokers,  Mechanical,  295. 


376 


INDEX 


Stop-valves,  249. 

Straw,  37. 

Strength  of  Riveted  Joint,  218. 

Strength  of  Rivets,  214. 

Superheated  Steam,  361. 

Table  I,  Specific  Heats  and  Densi- 
ties, 6. 

Table  II,  Latent  Heat  of  Fusion,  7. 

Table  III,  Latent  Heat  of  Evapora- 
tion, 8. 

Table  IV,  Factors  of  Evaporation,  12. 

Table  V,  Loss  by  Unburned  Coal  in 
Ash-pit,  23. 

Table  VI,  Total  Heats  of  Combus- 
tion, 29. 

Table  VII,  Weight  of  Coals,  35. 

Table  VIII,  Composition  of  Fuel-oils, 
51. 

Table  IX,  Composition  of  Fuel-gases, 
54. 

Table  X,  Fuel-values  of  Gases,  55. 

Table  XI,  Horizontal  Return-tubular 
Boilers,  £0. 

Table  XII,  Vertical-tubular  Boilers,  83. 

Table  XIII,  Steam-space,  122. 

Table  XIV,  Rates  of  Combustion,  131. 

Table  XV,  Relative  Rates  of  Com- 
bustion, 132. 

Table  XVI,  Rates  of  Combustion  for 
Chimney  Heights,  133. 

Table  XVII,  Greatest  Number  of 
Tubes  in  Horizontal  Boiler,  189. 

Table  XVIII,  Details  of  Riveted 
Joints,  223. 

Table  XIX,  Number  of  Bricks  in 
Boiler  Setting,  229. 

Table  XX,  Air-spaces  and  Thickness 
of  Grate-bars,  281. 

Table  XXI,  Heat  Losses,  Pipe  Cover- 
ings, 352. 

Table  XXII,  Savings  Due  to  Pipe 
Coverings,  354. 

Table  XXIII,  Net  Savings  Due  to 
Pipe  Coverings,  355. 

Table  XXIV,  Savings  Due  to  Hair 
Felt,  355. 


Table  XXV,  Loss  of  Heat  from  Bare 
Pipe,  356. 

Table  XXVI,  Variation  of  Loss  of 
Heat  with  Pressure,  356. 

Table  XXVII,  Loss  of  Heat,  Miscel- 
laneous Substances,  356. 

Table  XXVIII,  Comparison  of  Re- 
sults, 357. 

Temperature,  2. 

Temperature,  Effect  of— on  Mild  Steel, 
148. 

Temperature  of  Chemical  Union,  19, 
20. 

Temperature  in  Furnace,  56. 

Testing,  345. 

Tests  for  Boiler-plate  and  Bracing,  143. 

Tests  for  Nickel-steel  Rivet-rods  and 
Rivets,  146. 

Thermal  Unit,  4. 

Thermometers,  3. 

Thickness  of  Fire,  23. 

Thornycroft  Boiler,  113. 

Total  Heat  of  Evaporation,  9. 

Traps,  2S9. 

Trials,  Boiler,  346. 

Try-cocks,  273,  275. 

Tube  Expanders,  190. 

Tubes,  141,  186. 

Tubes,  Pitch  of,  94,  187. 

Turf,  36. 

Upright  Boiler,  79. 
Uptake,  286. 

Valves,  248. 

Vertical  Boiler,  79,  206. 

Volume  of  Air  for  Combustion,  25. 

Wasting,  a  Form  of  Corrosion,  319. 
Water-alarms,  274. 
Water-bottom,  105. 
Water  Evaporated  per  Foot  of  Heat- 
ing Surface,  66. 
Water-gauge,  273. 
Water-space,  120. 
Water  Surface,  123. 
Water-tubular  Boilers,  63,  106. 


INDEX 


377 


Water-tubular  Boilers,  Advantages 
and  Disadvantages  of,  111. 

Wear  and  Tear,  323. 

Weight  of  Air  per  Pound  of  Carbon, 
349. 

Weight  of  Boiler-plate,  Variation 
Allowed,  144. 

Weight  of  Water,  9. 

Welding,  224. 

Wet  Bridge,  103. 


Wet  Steam,  122,  348,  361. 
Wheel  Draft,  87. 
Wind-Pressures  on  Stacks,  329. 
Wood,  36. 
Wrought  Iron,  139. 

Yarrow  Boiler,  113. 
Zinc  Plates,  316,  322. 


^^T=^=^^^-^-^ 


YC   12766 


